System for chemical mechanical polishing having multiple polishing stations

ABSTRACT

An apparatus and associated methods for polishing semiconductor wafers and other workpieces that includes a polishing surfaces, such as pads mounted on respective platens, located at multiple polishing stations. Multiple wafer heads, preferably at least one greater in number than the number of polishing stations, can be loaded with individual wafers. The wafer heads are suspended from a rotatable support, which provides circumferential positioning of the heads relative to the polishing surfaces, and the wafer heads move linearly with respect to the polishing surface, for example oscillate radially within the rotatable support. A load/unload station may be located at a position symmetric with the polishing surfaces. The rotatable support can simultaneously position one of the heads over the load/unload station while the remaining heads are located over polishing stations for wafer polishing so that loading and unloading of wafers can be performed concurrently with wafer polishing. The multiple polishing stations can be used to sequentially polish a wafer held in a wafer head in a step of multiple steps. The steps may be equivalent, may provide polishes of different finish, or may be directed to polishing different levels. Alternately, more than one wafer may equivalently be polished at multiple polishing stations.

RELATED APPLICATIONS

This application is a divisional of Ser. No. 08/549,336, filed Oct. 27,1995, now issued as U.S. Pat. No. 5,738,574, and incorporated herein byreference. This application is also related to applications Ser. No.08/549,001, filed Oct. 27, 1995 and Ser. No. 08/549,607, filed Oct. 27,1995, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to an apparatus and method for chemicalmechanical polishing of semiconductor substrates using continuous orbatch processing. Various aspects of the invention includesimultaneously polishing two substrates at two polishing stations orsequentially polishing one substrate at two stations, whilesimultaneously another substrate is being loaded or unloaded from thesystem.

BACKGROUND OF THE INVENTION

Integrated circuit devices are typically formed on substrates, mostcommonly on semiconductor substrates, by the sequential deposition andetching of conductive, semiconductive, and insulative film layers. Asthe deposition layers are sequentially deposited and etched, theuppermost surface of the substrate, i.e., the exposed surface of theuppermost layer on the substrate, develops a successively moretopologically rugged surface. This occurs because the height of theuppermost film layer, i.e., the distance between the top surface of thatlayer and the surface of the underlying substrate, is greatest inregions of the substrate where the least etching has occurred, and leastin regions where the greatest etching has occurred.

This non-planar surface presents a problem for the integrated circuitmanufacturer. The etching step is typically prepared by placing a resistlayer on the exposed surface of the substrate, and then selectivelyremoving portions of the resist to provide the etch pattern on thelayer. If the layer is non-planar, photolithographic techniques ofpatterning the resist layer might not be suitable because the surface ofthe substrate may be sufficiently non-planar to prevent focusing of thelithography apparatus on the entire layer surface. Therefore, there is aneed to periodically planarize the substrate surface to restore a planarlayer surface for lithography.

Chemical mechanical polishing or planarizing (CMP) is one acceptedmethod of planarization. This planarization method typically requiresthat the substrate be mounted in a wafer head, with the surface of thesubstrate to be polished exposed. The substrate supported by the head isthen placed against a rotating polishing pad. The head holding thesubstrate may also rotate, to provide additional motion between thesubstrate and the polishing pad surface. Further, a polishing slurry(typically including an abrasive and at least one chemically reactiveagent therein, which are selected to enhance the polishing of thetopmost film layer of the substrate) is supplied to the pad to providean abrasive chemical solution at the interface between the pad and thesubstrate. For polishing of an oxide layer, the slurry is usuallycomposed of silica grit having diameters in the neighborhood of 50 nm.The grit is formed by fuming and is then placed in a basic solutionhaving a pH in the neighborhood of 10.5. The solution is then stronglysheared by blending so that the grit remains in colloidal suspension forlong periods. For metal polishing, the grit may be formed from eithersilica or alumina.

The combination of polishing pad characteristics, the specific slurrymixture, and other polishing parameters can provide specific polishingcharacteristics. Thus, for any material being polished, the pad andslurry combination is theoretically capable of providing a specifiedfinish and flatness on the polished surface. It must be understood thatadditional polishing parameters, including the relative speed betweenthe substrate and the pad and the force pressing the substrate againstthe pad, affect the polishing rate, finish, and flatness. Therefore, fora given material whose desired finish is known, an optimal pad andslurry combination may be selected. Typically, the actual polishing padand slurry combination selected for a given material is based on a tradeoff between the polishing rate, which determines in large part thethroughput of wafers through the apparatus, and the need to provide aparticular desired finish and flatness on the surface of the substrate.

Because the flatness and surface finish of the polished layer aredictated by other processing conditions in subsequent fabrication steps,throughput insofar as it involves polishing rate must often besacrificed in this trade off. Nonetheless, high throughput is essentialin the commercial market since the cost of the polishing equipment mustbe amortized over the number of wafers being produced. Of course, highthroughput must be balanced against the cost and complexity of themachinery being used. Similarly, floor space and operator time requiredfor the operation and maintenance of the polishing equipment incur coststhat must be included in the sale price. For all these reasons, apolishing apparatus is needed which has high throughput, is relativelysimple and inexpensive, occupies little floor space, and requiresminimal operator control and maintenance.

An additional limitation on polishing throughput arises because thepad's surface characteristics change as a function of the polishingusage, and the pad also becomes compressed in the regions where thesubstrate was pressed against it for polishing. This condition, commonlyreferred to as "glazing", causes the polishing surface of the polishingpad to become less abrasive to thereby decrease the polishing rate overtime. Glazing thus tends to increase the polishing time necessary topolish any individual substrate. Therefore, the polishing pad surfacemust be periodically restored, or conditioned, in order to maintaindesired polishing conditions and achieve a high throughput of substratesthrough the polishing apparatus. Pad conditioning typically involvesabrading the polishing surface of the pad to both remove anyirregularities and to roughen the surface.

Pad conditioning, although it raises the average polishing rates,introduces its own difficulties. If it is manually performed, itsconsistency is poor and it incurs operator costs and significantdowntime of the machinery, both decreasing the cost adjusted throughput.If the pad conditioning is performed by automated machinery, care mustbe taken to assure that the surface abrading does not also gouge anddamage the polishing pad. Furthermore, if the relative motion betweenthe conditioning tool and pad is primarily provided by the pad rotation,the relative velocity and dwell time varies over the radius of the pad,thus introducing a radial non-uniformity into the reconditioned pad.

A further limitation on traditional polishing apparatus throughputarises from the loading and unloading of substrates from the polishingsurface. One prior art attempt to increase throughput, as shown by Gillin U.S. Pat. No. 4,141,180, uses multiple polishing surfaces forpolishing the substrate to thereby allow optimization of polishing rateand finish with two different pad or slurry combinations. A mainpolishing surface and a fine polishing surface are provided within thedescribed polishing apparatus at a polishing station. A single polishinghead, controlled by a single positioning apparatus, moves a singlesubstrate between the different polishing stations on the apparatus.

Another method of increasing throughput uses a wafer head having aplurality of substrate loading stations therein to simultaneously load aplurality of substrates against a single polishing pad to enablesimultaneous polishing of the substrates on the single polishing pad.Although this method would appear to provide substantial throughputincreases over the single substrate style of wafer head, several factorsmilitate against the use of such carrier arrangements for planarizingsubstrates, particularly after deposition layers have been formedthereon. First, the wafer head holding the wafer being polished iscomplex. To attempt to control the force loading each substrate againstthe pad, one approach floats the portion of the head holding the wafer.A floating wafer holder necessitates a substantial number of movingparts and pressure lines must be included in the rotating and movinggeometry. Additionally, the ability to control the forces pressing eachindividual substrate against the pad is limited by the floating natureof such a wafer head assembly, and therefore is a compromise betweenindividual control and ease of controlling the general polishingattributes of the multiple substrates. Finally, if any one substratedevelops a problem, such as if a substrate cracks, a broken piece of thesubstrate may come loose and destroy all of the other substrates beingpolished on the same pad.

Polishing throughput is yet further limited by the requirement thatwafers be washed at the end of polishing and sometimes between stages ofpolishing. Although washing time has been limited in the past bysimultaneously washing multiple wafer head, insofar as the washingrequires additional machine time over that required for polishing,system throughput is adversely affected.

Therefore, there is a need for a polishing apparatus which enablesoptimization of polishing throughput, flatness, and finish whileminimizing the risk of contamination or destruction of the substrates.

The high-speed polishing required for a high-throughput polishingapparatus imposes severe restrictions and requirements on the polishingapparatus. The mechanical forces are large, but minute scratchesincurred in polishing are fatal to integrated circuits. Hence, thedesign must control and minimize mechanical aberrations. The environmentof CMP processing is harsh so that the machinery must be carefullydesigned to lengthen lifetime and reduce maintenance. Also, the slurry,when allowed to dry on the wafer or any part of the apparatus, tends toform a hardened layer that becomes very difficult to remove. In general,a high-throughput apparatus needs to be easy to operate, require littleoperator intervention, be easily serviced for regular or unscheduledmaintenance, and not be prone to failure or degradation of its parts.

If a polishing system is to be commercialized, it must be flexible andadaptable to a number of different polishing processes. Differentintegrated-circuit manufacturers prefer different polishing processesdependent on their overall chip design. Different layers to beplanarized require distinctly different polishing processes, and thechip manufacturer may wish to use the same polishing system for twodifferent polishing processes. Rather than designing a polishing systemfor each polishing process, it is much preferable that a single designbe adaptable to the different processes with minimal changes ofmachinery.

SUMMARY OF THE INVENTION

The present invention provides a chemical mechanical polishingapparatus, and a method of using the apparatus, to provide a high rateof throughput of substrates with improved flatness and surface finish ofthe planarized substrate.

The present invention further provides great flexibility in thepolishing processes performed sequentially at multiple polishingstations.

In one configuration according to the invention, multiple, for examplefour, identical wafer heads are mounted equally distributed about thecenter support of a carousel support plate. The centrally supportedcarousel frame when rotated positions the wafer heads and thesubstrates. Each head can rotate independently and can independentlyoscillate radially in slots formed in the head plate. Because thecarousel assembly which holds the wafer head is vertically fixed,raising or lowering the wafer from the surface of the polishing padrequires relative motion between the wafer receiving surface of thewafer head and the vertically fixed support of the carousel arm. In oneconfiguration relative movement between a wafer receiving member of thewafer head and a top member of the wafer head supplies the neededvertical motion.

In use, multiple ones, for example, three, of the wafer heads aresimultaneously positioned above polishing stations while the remainingwafer head is positioned over a transfer station. Each polishing stationis complete with an independently rotating platen supporting a polishingpad whose surface is wetted with an abrasive slurry which acts as themedia for polishing.

Each polishing pad is conditioned by an independently rotatingconditioner head which is swept in an oscillatory motion over an arcuatepath between the center of the polishing pad and its perimeter. Theconditioner arm presses the conditioning plate mounted on its endagainst the pad to condition the pad. A conditioner apparatus accordingto the invention provides for an automatic increase in conditioningpressure to the pad in areas where the pad has become glazed, and anautomatic reduction in conditioning pressure to the pad in areas wherethe pad is not glazed (the sensing of the coefficient of frictionbetween the conditioner head and the pad providing immediate feedbackcausing the conditioning pressure to change accordingly).

In use, one of the wafer heads is positioned above a transfer stationfor loading and unloading wafers to and from the heads while the otherheads are positioned above the polishing stations and their wafer arebeing polished. The transfer station can also be used to align wafersand to wash the wafers and the wafer heads.

An aspect of the invention provides a polishing process using multiplepolishing pads. The apparatus thus includes a first polishing surface,which produces a first material removal rate and a first surface finishand flatness on the substrate, and at least one additional polishingsurface, which produces a second surface finish and flatness on thesubstrate. The multiple pads can be used in an in-line process in whichthe pads have substantially similar polishing characteristics but awafer is nonetheless sequentially polished on the different pads. Thedivision of equivalent polishing between different polishing padsreduces the loading and unloading time. Alternatively, the multiple padscan be used in a multi-step process in which the pads have differentpolishing characteristics and the wafers are subjected to progressivelyfiner polishing or the polishing characteristics are adjusted todifferent layers to be progressively encountered during polishing, forexample, metal lines underlying an oxide surface.

The central carousel support plate includes a series of radial slots inwhich the wafer head assemblies can oscillate between an inner radialposition and an outer radial position as the wafer heads and attachedwafers are independently rotated by wafer head rotation motors and aresimultaneously pressed against the independently rotating polishing padsby pressure independently applied by each wafer head. The slotted designreduces the mechanical rigidity required to reduce vibration. Also, itallows easy maintenance of the wafer heads.

The placement and movement of wafer cassettes and substrates and theduration of polishing or cleaning performed at each station arepreferably controlled by a controller, such as a microprocessor, whichis programmed to direct the positioning and loading of the substratesand to provide optimal polishing finish, flatness, and throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an embodiment of the polishing apparatusof the invention;

FIG. 2 is an exploded view of the polishing apparatus of FIG. 1 showingthe upper housing and mechanism separated from the lower housing andmechanism;

FIG. 3 is a graph schematically illustrating glazing causes polishingrates to decrease with time;

FIG. 4 is a schematic illustration of the variations in polishing ratesover the areas of a rotating wafer and a rotating pad;

FIGS. 5A, 5B, 5C, 5D, 5E, and 5F schematically show the progressivemovement of wafers as they are sequentially loaded and polished in thecarousel carrier polishing apparatus according to the invention;

FIGS. 6A, 6B, 6C, and 6D show the movement of the wafer from and to thetransfer-cleaning station as is seen in FIGS. 5E and 5F and show theactual movement of substrates in the polishing carousel;

FIG. 7 is an exploded view of the carousel of FIG. 2;

FIG. 8 is a top view of the carousel according to the invention with theupper housing removed;

FIG. 9 is a cross section of the wafer head system of FIG. 8 taken atline 9--9 of FIG. 8, including one type of wafer head;

FIG. 10 is a close up view of the wafer head to shaft housing connectionas shown in FIG. 9;

FIGS. 11 and 12 are cross-sectional views of a second type of waferhead;

FIG. 12A is a cross-sectional view a third type of wafer head related tothat of FIGS. 11 and 12;

FIG. 13 is a cross-sectional view of a novel rotary union;

FIGS. 14A, 14B, and 14C show the progressive positions of the shaftfollower slot splash shield plate as a wafer head assembly oscillatesradially from its innermost position to its outermost position;

FIGS. 15A, 15B, and 15C show progressive end cross sectional views ofthe shaft follower slot splash shield plate as a wafer head assemblyoscillates radially from its innermost position to its outermostposition corresponding to the views shown in FIGS. 14A, 14B, and 14C;

FIGS. 16A, 16B, and 16C show progressive side cross sectional views ofthe operation of the splash plates taken along the radial axis of acarrier arm and corresponding to the views shown in FIGS. 14A, 14B, and14C;

FIGS. 17A, 17B, and 17C show progressive perspective views of the splashplates as shown in FIGS. 14A, 14B, and 14C;

FIG. 18 shows a top view of the polishing apparatus according to theinvention with the carousel head plate and wafer head assembliesremoved;

FIG. 19 shows a cross sectional view of a platen of FIG. 18 taken at19--19;

FIG. 20 is an enlarged cross-sectional view of the reservoir portion ofthe platen of FIG. 19;

FIG. 20 is a yet further enlarged cross-sectional view of the pneumaticpump of the reservoir of FIG. 20;

FIG. 22 is a schematical cross-sectional view of an overhead slurrydispenser located to the side and over a platen;

FIG. 23 is a plan view of the overhead slurry dispenser of FIG. 22;

FIG. 24 is an enlarged elevational view of the dispensing end of theoverhead slurry dispenser of FIG. 22;

FIG. 25 is a schematical diagram of the slurry distribution system;

FIGS. 26A, 26B, 26C, 26D, and 26E are lateral cross-sectional views ofthe intermediate washing station located between adjacent polishingplaten. The sequence of these five similar views show the progressiveaction of a wafer head and attached wafer being washed at theintermediate washing station;

FIG. 26F is a longitudinal side view taken at 26F--26F of FIG. 26D ofthe intermediate washing station of FIGS. 26A through 26E;

FIG. 26G is a top plan view taken at 26G--26G of FIG. 26E of theintermediate washing station of FIGS. 26A through 26F;

FIG. 27 is a side cross-sectional view of a second embodiment of theintermediate washing station;

FIG. 28 is a plan view of the washing station of FIG. 27;

FIG. 29 shows the side cross sectional view of a polishing padconditioner apparatus according to the invention;

FIG. 30 shows an exploded perspective view of the conditioning disk fitinto the conditioner head;

FIG. 31 shows a close up view of the conditioner head shown in FIG. 29;

FIG. 32 shows a schematic view of a prior art configuration for aconditioner head apparatus;

FIG. 33 shows a schematic view of a conditioner head apparatus accordingto the invention;

FIG. 34 shows an exploded view of the conditioner support/drive endconnection with the conditioner arm and the drive sheave;

FIG. 35 shows a cross-sectional view, partly in plan schematic view, ofthe conditioner arm support and drive mechanism;

FIGS. 36A, 36B, and 36C shows the progressive steps as a conditionerapparatus raises its conditioner head out of its washing cup and lowersthe conditioner head into position on the polishing pad;

FIG. 37 shows a side cross sectional view of the conditioner headwashing cup according to the invention;

FIG. 38 shows a close up top view of the washing station according tothe invention;

FIGS. 39A, 39B, and 39C show a top view of a polishing position showingthe general relative movements of the polishing platen, wafer head, andconditioner head as shown in FIGS. 36A-36C;

FIG. 40 shows a perspective view of a wafer transfer alignment cleaningstation according to the invention;

FIG. 41 shows a top view of the wafer transfer alignment cleaningstation of FIG. 40;

FIG. 42 shows a perspective view in partial cross-section of the wafertransfer alignment cleaning station of FIG. 40, showing the pneumaticactuators which are used to actuate the alignment jaws to align thewafer to the wafer head;

FIG. 43 shows a partial perspective cross-section of the wafer transferalignment cleaning station of FIG. 40, showing the center and perimeterfluid passages to spray nozzles and suction ports;

FIG. 44 shows a cross-sectional view of the transfer station pedestaland surrounding wash basin;

FIG. 44A shows an enlarged cross-sectional view of the part of FIG. 44illustrating the connection between the pedestal column and the basinhousing;

FIG. 45 shows a closeup sectional view in perspective of the alignmentjaw to alignment yoke connection of FIG. 42;

FIG. 46 shows a perspective view of the spider assembly at the lower endof the pedestal shaft;

FIGS. 47A, 47B, 47C, 47D, and 47E show side elevational cross-sectionalviews of progressive steps according to the invention taken to align andload a wafer into the wafer receiving recess of a wafer head forsubsequent polishing;

FIGS. 48A, 48B, and 48C provide top cross sectional schematic views ofthe wafer transfer cleaning station showing the alignment of a waferbeing loaded on a wafer head, corresponding to the respective views ofFIGS. 47A, 47B, and 47C;

FIGS. 49A, 49B, and 49C; their respective counterparts 50A, 50B, and50C; and 51A, 51B, and 51C show side cross-sectional, partial crosssectional, and top cross sectional and schematic views of the wafertransfer-cleaning station and the check valve in the pedestal, inprogressive steps as a wafer and the lower portion of a wafer head towhich the wafer is still initially attached is thoroughly rinsed by allavailable nozzles; and in progressive steps the wafer is released fromthe head and held on the pedestal by vacuum and rinsing of the assemblyin this configuration is performed before removal of the wafer from thepolishing apparatus by a robot blade;

FIG. 52 shows a side cross sectional view showing the head plate inposition over the polishing stations and one wafer head assembly inposition over and within a wafer alignment transfer cleaning apparatusaccording to the invention, for example taken at line 52--52 of FIG. 2;

FIG. 53 shows a perspective view of a gear locking assembly at thebottom of the carousel;

FIG. 54 shows a front partial cross sectional schematic view of a waferloading apparatus according to the invention;

FIG. 55 shows a perspective view of an "L" shaped member which includesthe robot blade and a wafer cassette tray lifting claw as used for thedevice of FIG. 53;

FIG. 56 shows a perspective view of the bottom of the robot blade ofFIG. 55;

FIG. 57 shows a back partial cross sectional schematic view of theblade, claw, and bottom of the arm of the wafer loading apparatus ofFIG. 54;

FIG. 58 shows a side plan view of the robot blade of FIG. 54;

FIGS. 59 and 60 show respectively top and bottom partial cross-sectionalplan views of the robot blade of FIG. 58;

FIG. 61 shows a simplified exploded perspective view of the descendingarm and wrist assembly of the wafer loading apparatus of FIG. 54;

FIG. 62 shows a simplified exploded top perspective view of the overheadtrack of the wafer loading apparatus of FIG. 54;

FIG. 63 shows a perspective view of an end of the overhead track of FIG.62;

FIG. 64 shows a top partial plan view of the overhead track of FIG. 54;

FIG. 65 shows an end partial cross sectional schematic view of the waferloading apparatus of FIG. 54;

FIG. 66 shows a end view of the wafer and cassette loading apparatusaccording to the invention showing the location of the wafer bath andwafer cassettes in the wafer bath with respect to the polishingapparatus;

FIG. 67 shows an axial cross-sectional view of tub holding one or morewafer cassettes in a liquid bath;

FIG. 68 shows a side view of a top of a weir controlling the surfacelevel of the bath in the tub of FIG. 67;

FIG. 69 shows an elevational view of a support rail of the tub of FIG.67;

FIGS. 70A, 70B, 70C, 70D, and 70E are schematic perspective viewsshowing progressive steps and movement of a robot blade according to theinvention by which wafers are loaded and unloaded into and from thepolishing apparatus;

FIGS. 71A, 71B, and 71C show the movement of the cassette lifting forkof the "L" shaped member as it lifts the wafer cassette; and

FIGS. 72A, 72B, and 72C show the progressive movement of the wafercassettes such that in a batch operation particular cassettes can bemove to provide progressive and continuous polishing and utilization ofthe apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This description will first give an overview of the system and a generaldescription of the processing steps. Then, the individual sub-systemsand the detailed processes will be further described.

Apparatus Overview

FIG. 1 shows a perspective view of an apparatus according to theinvention. A polishing system 10 includes a polishing apparatus 20adjacent to a wafer loading apparatus 30. Wafers 40 brought to thesystem 10 in a cassette 42, which is immediately stored in a tub 34 soas to keep the wafers wet. The wafers 40 are individually loaded fromthe cassette 42 into the wafer polishing apparatus 20, which polishesthem and then returns them to the original cassette 42 or another one inthe tub 34. The figure does not show a wall interposed between thepolishing apparatus 20 and the wafer loading apparatus 30 so as tocontain the slurry and other polishing debris within polishing apparatus20 and away from the tub 34. An unillustrated sliding door in the wallis opened for transfer of wafers between the two apparatus 20 and 30.The wall may act as the barrier between the clean room containing thewafer loading apparatus 30 and a dirtier area containing the polishingapparatus 20.

The polishing apparatus 20 includes a lower machine base 22 with a tabletop 23 mounted thereon and a removable upper outer cover 24 surroundinga series of polishing stations 50a, 50b, and 50c. As shown in theexploded isometric view of FIG. 2, a fence 25 surrounds the table top 23to contain the liquids and slurry being thrown about and which aredrained through unillustrated drains in the table top.

Each polishing station 50a, 50b, or 50c includes a rotatable platen 52on which is placed a polishing pad 54, and it further includes anassociated pad conditioner apparatus 60a, 60b, or 60c, each with arotatable arm 62 holding a conditioner head 64 and an associated washingbasin 68 for the conditioner head 62. The base 22 also supports atransfer station 70 positioned in a square arrangement with the threepolishing stations 50a, 50b, and 50c. The transfer station 70 servesmultiple functions of receiving individual wafers 40 from the loadingapparatus 30, possibly rinsing them, loading them to wafer heads (to bedescribed later) which hold them during polishing, receiving the wafers40 back from the wafer heads, washing them, and finally transferringthem back to the loading apparatus 30. It also washes the wafer headafter its wafer has been unloaded.

Two intermediate washing stations 80a and 80b are located betweenneighboring ones of the polishing stations 50a, 50b, and 50c, and athird washing station 80c may be located between the last polishingstation 50c and the transfer station 70. These rinse a wafer 40 as itpasses from one polishing station to another and to the transfer station70 and may effectively buff the wafer 40 as well.

A rotatable multi-head carousel 90 includes four wafer head systems100a, 100b, 100c, and 100d which receive and hold wafers 40 and polishthem by pressing them against respective polishing pads 54 held on theplatens 52 at the respective polishing stations 50a, 50b, and 50c. Thecarousel 90, which is in the shape of a cross because the area betweenits arms is removed, is supported on a stationary center post 902 and isrotated thereon about a carousel axis 904 by a motor assembly locatedwithin the base 22.

In this configuration according to the invention, the four identicalwafer head systems 100a, 100b, 100c, and 100d are mounted on a carouselsupport plate 906 at equal angular intervals about the carousel axis904. The center post 902 centrally supports the carousel support plate906 and allows the carousel motor to rotate the carousel support plate906, the wafer head systems 100a, 100b, 100c, and 100d, and the wafers42 attached thereto about the carousel axis 904.

Each wafer head system 100a, 100b, 100c, or 100d includes a wafer head110 that is rotated about its own axis by a head-rotation motor 1002connected to it by a shaft. The heads 110 can rotate independently asdriven by their dedicated head-rotation motors 1002 (shown in FIG. 2 bythe removal of one carousel quarter-cover 908), and can furtherindependently oscillate radially in slots 910 formed in the carouselsupport plate 906. Raising or lowering wafers attached to the bottom ofthe wafer heads 110 is performed within the wafer head systems 100. Anadvantage of the overall carousel system is that very little verticalstroke is required of the wafer head 110 to accept the wafers andposition them for polishing and washing. What little vertical stroke isrequired can be accommodated within the lowermost member at the very endof the wafer head 110. An input control signal causes relative motion(extension and retraction of the head) between a wafer head lower memberwhich includes a wafer receiving recess and a vertical stationary waferhead upper member according to an input control signal (e.g., apneumatic, hydraulic, or electrical signal).

During the actual polishing, the wafer heads 110 of three of the waferhead systems, e.g., 100a, 100b, and 100c, are positioned at and aboverespective polishing stations 50a, 50b, and 50c, each having anindependently rotatable platen 52 supporting a polishing pad 54 whosesurface is wetted with an abrasive slurry which acts as the media forpolishing the wafer 40. During polishing, the wafer head systems 100a,100b, and 100c independently oscillate along respective radii of thecarousel 90 so that the associated wafer heads 110 move along a diameterof a respective polishing pad 54. In a typical process, the sweep axisof a wafer head 110 is aligned to the center of the polishing pad 54.

In use, the wafer head 110, for example, that of the fourth wafer headsystem 100d, is initially positioned above the wafer transfer station70. When the carousel 90 is rotated, it positions different wafer headsystems 100a, 100b, 100c, and 100d over the polishing stations 50a, 50b,and 50c and over the transfer station 70. The carousel 90 allows eachwafer head system 100 to be sequentially located first over the transferstation 70, then over one or more of the polishing stations 50, and thenback to the transfer station 70.

Each polishing pad 54 can be continuously or periodically conditioned byone of the pad conditioner apparatus 60, each having an independentlyrotating conditioner head 64 attached to the conditioner arm 62. Anabrasive conditioning plate or a similar conditioning surface needs tobe included at the bottom of the conditioner head 64. The arm 62 sweepsthe conditioner head 64 across the associated polishing pad 54 in anoscillatory motion generally between the center of the polishing pad 54and its perimeter. The conditioner head 64 is pressed against the pad 54to abrade and condition the pad so that it thereafter effectivelypolishes any wafer 40 pressed against it while it is rotating.

In the wafer loading system 30, shown in FIG. 1, the cassette 42 isfirst transferred from a holding station 32 to a holding tub 34 filledwith a liquid bath 302 such as deionized water to a level to submersethe cassettes 42 and the wafers 40 contained therein. Then, individualwafers 40 to be polished are withdrawn from the wafer cassette 42 in thetub 34 to the polishing apparatus 20. A rotatable, extensible descendingarm 35 descending pending from an overhead track 36 includes at itsdistal end a wrist assembly 37 including both a wafer blade 38 and acassette claw 39. The cassette claw 39 can move cassettes 42 between theholding station 32 and the tub 34, and the wafer blade 38 can move andreorient wafers 40 between the cassettes 42 in the tub 34 and thetransfer station 70. Although FIG. 1 and the remaining figures show theholding station 32 disposed on a side of the machine base 22 away fromthe transfer station 70, this illustration is so arranged only forclarity. In fact, the corner of the machine base 22 holding the transferstation 70 is pulled in relative to its other corners. Hence, theholding station 32 is advantageously disposed in the more open area atthe corner of the transfer station 70 outside the machine base 22.

General Polishing Processes

The apparatus outlined above can be used for a number of different typesof polishing sequences. Three principal polishing processes are thein-line process, the multi-step process, and the batch process.

The in-line process divides the polishing operation into multiple stepsat different polishing stations 50, and the steps are substantiallyequivalent. In the simplest case, the same type of polishing pad and thesame slurry are used at the three polishing stations 50a, 50b, and 50c.As will be described in more detail below, a wafer head 110 carries awafer to each polishing station in sequence, and one-third of the totalpolishing is performed at each polishing station.

A motivation for the in-line polishing system arises from the need tocondition a pad before a complete polishing operation is completed.Polishing pads tend to become glazed during polishing. As schematicallyillustrated in the graph of FIG. 3, the polishing removal rate begins ata high level for a new or freshly conditioned pad, but the removal ratedecreases with cumulative polishing time for the pad. To achieve highthroughput, the pad is conditioned before the removal ratdecreases withcumulative polishing time for the pad. To achieve high throughput, thepad is conditioned before the removal rate falls to too low a level. Theperiod between conditioning depends on the polishing pad, the polishingprocess, and the material being removed from the wafer. An important useof CMP is planarizing silicon dioxide, a very hard material, and up to 2μm of silicon dioxide may need to be removed for some semiconductorfabrication processes. If this thickness corresponds to a polishing timefar down the curve of FIG. 3, then the pad needs to be conditioned atleast once during the polishing. Since pad conditioning often requiresthe wafer to be removed from the pad and the wafer head system to bemoved away from at least the center of the pad, a break in the polishingfor pad conditioning can be used to move the wafer to another equivalentpolishing station.

A yet further motivation for the in-line process is that the loading,unloading, and washing being performed at the transfer station 70constitute an overhead time for the process. If this overhead isperformed while the wafer heads are positioned where no polishing isbeing performed, polishing throughput is decreased. With the threepolishing stations 50a, 50b, and 50c and the transfer station 70arranged at equivalent positions around the carousel, the overhead atthe transfer station 70 can be concurrently performed while three wafersare being polished. The overhead is thus reduced to the time required tomove a wafer between the polishing stations and between them and thetransfer station.

A further advantage of the in-line process in dividing up the polishingbetween equivalent polishing stations is that irregularities inparticular polishing stations tend to average out over the differentpolishing stations.

The multi-step process divides a polishing process into multiple anddifferent steps, typically with gradated polishing. For example, thefirst polishing station 50a may perform a rough polish on the wafer, thesecond polishing station 50b may perform a fine polish, and the thirdpolishing station 50c may buff the wafer. Buffing is a very gentlepolish which primarily removes extraneous loose matter from the surface.The intensity of polishing may be varied by the slurry composition, padmaterial, and other polishing parameters. Of course, the inventionprovides for an integrated multi-step process with low overhead.However, the multi-step process has inherent throughput problems becausenot all three polishing steps require the same time. Usually, the roughpolish requires significantly more time than the fine polish or buffing.Therefore, system throughput is limited by the rough polish while theother two polishing stations may lie idle for long periods. Similarscheduling problems exists when the different polishing stations arebeing used for different steps of the polishing process, for example,the previously mentioned polish directed to silicon dioxide followed bya polish directed to a metal layer.

The batch process completely polishes multiple wafers at respectivepolishing stations. In the apparatus of FIG. 1, the same type of pad ismounted at and the same type of slurry supplied to the three polishingstations 50a, 50b, and 50c, and each wafer is completely polished at onepolishing station. That is, three unpolished wafers are simultaneouslypresented to the three polishing stations. The operations at thetransfer station present a high overhead in a batch process, but theapparatus of FIG. 1 at least allows the loading, unloading, and washingof one wafer to be performed while polishing is on going with thesimilar operations for the other two wafers necessarily interruptingpolishing.

The distinctions between in-line, multi-step, and batch processes arenot clearly defined, and a chosen process may have aspects of more thanone. For example, two of the polishing stations 50a and 50b may be usedfor equivalent in-line or batch polishing, and the third polishingstation 50c for a multi-step fine polish or buff. As will be describedlater, the three intermediate wash stations 80a, 80b, and 80c can beused for a short buffing, wafer washing or even light polishing step. Inthis situation, batch processing for the polishing stations becomes morefeasible with a higher utilization of the expensive parts of theapparatus.

The invention provides a significant process advantage in allowingover-center polishing, that is, the wafer 40 can be swept across thecenter of the rotating polishing pad 54. Polishing using a rotatingwafer 40, a rotating pad 54, or a combination thereof suffers from aninherent non-uniformity. Namely, as illustrated in FIG. 4, both thewafer 40 and the pad 54 are rotating about their respective centers 40aand 54a. Polishing removal rates are usually proportional to therelative velocity between the wafer 40 and pad 54, and the velocity of arotating object increases with the radius. Therefore, the outer portionof the rotating wafer 40 will be polished more quickly than its innerportion. Similarly, the outer portion of the pad 54 polishes the wafermore quickly than does the inner portion of the pad. The divisions ofthe wafer 40 and pad 54 into two zones is overly simplistic since thereis a continuous gradation. To reduce these inherent non-uniformities,the sweep pattern and timing of the wafer 40 over the pad 54 can beoptimized, as has been disclosed by Tolles et al. in U.S. patentapplication, Ser. No. 08/497,362, filed Jun. 30, 1995, now issued asU.S. Pat. No. 5,599,423. The ability to sweep the wafer 40 over thecenter 54a of the pad to a position 40c on the other side of pad center54a provides another degree of freedom in the optimization. Theadditional degree of freedom from over-center polishing has not beentypically available in commercially available wafer polishing systems.

The in-line process will now be described in detail because of itsimportance. FIGS. 5A, 5B, 5C, 5D, 5E, and 5F show a sequence of sixphases between which the carousel 90 rotates. The description beginswith the insertion of a wafer (W) and continues with the subsequentmovement of wafer head systems 100a, 100b, 100c, and 100d supported onthe carousel support plate 906 of the carousel 90.

As shown for the first phase in FIG. 5A, a first wafer W#1 is loadedfrom the loading apparatus 30 to the transfer station 70, which loadsthe wafer into a wafer head 110, e.g., that of the wafer head system100a. The carousel 90 is then rotated counter-clockwise on thesupporting center post 902 so as to position the first wafer head system100a and its wafer W#1 over the first polishing station 50a, as shownfor the second phase stage in FIG. 5B. The polishing station 50a thereperforms a first-stage polish of the wafer W#1. While the firstpolishing station 50a is polishing the first wafer W#1, a second waferW#2 is being loaded from the loading apparatus 30 to the transferstation 70 and from there to the second wafer head system 100b, nowpositioned over the transfer station 70.

After the completion of the second phase of FIG. 5B, the carousel 90 isagain rotated counter-clockwise so that, as shown for the third phase inFIG. 5C, the first wafer W#1 is positioned over the second polishingstation 50b and the second wafer W#2 is positioned over the firstpolishing station 50a. The third wafer head system 100c is positionedover the transfer station 70, from which it receives a third wafer W#3from the loading system 30. During the third phase of FIG. 5C, bothwafers W#1 and W#2 are being polished at respective stations 50a and50b. To enter a fourth phase, as illustrated in FIG. 5D, the carousel 90again rotates counter-clockwise by 90° so as to position wafer W#1 overthe third polishing station 50c, the second wafer W#2 over the secondpolishing station 50b, and the third wafer W#3 over the first polishingstation 50a while the transfer station 70 receives a fourth wafer W#4from the loading apparatus 30. After the completion of the polishing ofthe third phase during which the first wafer W#1 receives a third-stagepolish, the second wafer W#2 receives a second-stage polish, and thethird wafer W#3 receives a first-stage polish, then the carousel 90 isagain rotated. However, rather than being rotated counter-clockwise by90°, the carousel 90 is rotated clockwise by 270° in order to avoid theneed to use rotary couplings and to allow simple flexible fluid andelectrical connections to the carousel 90 through flexible butcontinuous lines. This equivalent rotation, as illustrated in FIG. 5E,places the first wafer W#1 over the transfer station 70, the secondwafer W#2 over the third polishing station 50c, the third wafer W#3 overthe second polishing station 50b, and the fourth wafer W#4 over thefirst polishing station 50a. While the other wafers W#2, W#3, and W#4are being polished, the first wafer W#1 is washed at the transferstation 70 and is loaded from the first wafer head system 100a back tothe loading apparatus 30 and thence back to its original location in thecassette 42, and a fifth wafer W#5, as illustrated in FIG. 5F is loadedonto the first wafer head system 100a. After this phase, the process isrepeated with a 90° counter-clockwise rotation.

This description has not included the processing sequence in which thecarousel stops with the wafer heads located between platens at theintermediate washing stations to rinse the wafers between polishingstages or after completion of polishing.

This description is applicable both to a multi-step polishing system orto an in-line process involving substantially similar polishing at thedifferent stations. In the multi-step system, the multiple stages ofpolishing involves progressively finer polishing or polishing directedto different layers by means of variations of the pad structure orslurry composition. In the in-line process, each of the multiplepolishing stations performs substantially similar polishing on the samewafer and for a substantially equal time. The in-line process isadvantageous in that the overhead time per wafer associated with loadingand unloading is reduced by the multiplicity of polishing stations.Also, any non-uniform polishing introduced by one polishing station islikely to be averaged out by the other polishing stations.

FIGS. 5A, 5B, 5C, and 5D show further details of the movement of thecarousel 90 between the positions of FIGS. 5D and 5E. In FIG. 6A, thesecond, third, and fourth wafers W#2, W#3, and W#4 are being polished astheir juxtaposed pads 54 and platens 52 are rotating while the firstwafer W#1 is being washed at the transfer station 70. In FIG. 6B, thefirst wafer W#1 is loaded back to its cassette 42, and in FIG. 6C afifth wafer W#5 is loaded from its cassette 42 to the transfer station70, at which it is washed. All this time, the other three wafers W#2,W#3, and W#4 continue to be polished. In FIG. 6D, the carousel 90rotates by about 45° so that the second, third, and fourth wafers W#2,W#3, and W#4 lie over respective intermediate washing stations 80c, 80b,and 80a. In a process to be described more fully later, the two waferhead systems 100b, 100c, and 100d stepwise rotate their respectivewafers over the associated washing stations 80a, 80b, and 80c so as torinse any residual slurry and debris from a former polishing station 50so as to not contaminate a subsequent polishing station 50. A furtherwashing station 80 may be positioned between the transfer station 70 andthe first polishing station 50a to rinse the wafer prior to polishing.This pre-rinse can be performed without any additional overhead timeover that already consumed by the intermediate washing stations 80a and50b. After rinsing, the next carousel rotation of 45° is completed andpolishing continues.

The various subsystems will now be described in more detail.

Carousel

FIG. 7 shows an exploded view of the carousel 90 in which the quarterouter covers 908 has been removed. The center post 902 supports thelarge, thick (approx. 23/8" (6 cm)) carousel support plate 906(preferably made of aluminum). The carousel support plate 906 and mostof the structure of the carousel 90 is arranged in the shape of a crosswith four arms fixed at equal angular intervals 90° for the four-headconfiguration. The carousel support plate 906 includes four open-endedslots 910 extending radially and oriented 90° apart; FIG. 2 showsinstead a lower cover having a closely related closed-end slot 948. Thetop of the carousel head support plate 906 supports a set of four pairedslotted wafer head support slides 908, also shown in the top plan viewof FIG. 8 and the side cross section of FIG. 9. The slides 908 arealigned with and slide along the respective slots 910 in the carouselsupport plate 906 to freely move radially with respect to the center ofthe carousel support plate 906. Each slide 908 is supported by a linearbearing assembly 912, two of which bracket the slot 906. Each linearbearing assembly 912, as shown in cross section in FIG. 9, includes arail 914 fixed to the carousel support plate 906 and two linear guides916 (only one of which is illustrated on each side) with ball bearings917 rolling in between the grooves of the rail 914 and guides 916.Although not distinctly illustrated, two linear guides 916 are matedwith each rail 914 to provide free and smooth movement between them. Thelinear bearing assemblies 912 permit the slides 908 and whatever isattached thereto to freely move along the slots 910 in the carouselsupport plate. As shown in the top plan view of FIG. 8, a bearing stop917 is anchored to the outer end of one of the rails 914 to act as asafeguard to prevent the slide 908 from accidentally coming off the endof the bearing rails 914.

As shown in the top plan view of FIG. 8 and the cross section of FIG. 9,one side of each slider 908 contains an unillustrated recirculating ballthreaded receiving cavity (or nut) fixed to the slide 908 near itsmedial end. The threaded cavity or nut receives a lead screw 918 drivenby a motor 920, the sweep motor, mounted on the carousel support plate906. Turning the lead screw 918 causes the slide 908 to move radially.The four sweep motors 920 are independently operable, as illustratedbest in the top plan view of FIG. 8, thereby enabling separate movementof the four slides 908 along the slots 910 in the carousel support plate906.

An optical position sensor is attached to a side of each slide 908, asillustrated at the lower left of FIG. 8. A position flag 924 having ahorizontally extending fin 926 is attached to the worm side of eachslide 908. An optical sensor 928 in conjunction with the position flag924 provides center position sensing of the sweep motor 920. The sensor928 is fixed to the carousel support base 906 at a height such that thefin 926 passes through the trigger gap of the sensor 928. Further, it isfixed at a linear position along the slot 910 and has length such thatthe fin 926 obstructs trigger gap of the optical sensor 928 for one-halfof its travel, for example, center to innermost position and does notobstruct it from the center to outermost position. The transition at thecenter calibrates the system. Although the slide position is nominallymonitored by the input to the slide motor 920 or an encoder attachedthereto, such monitoring is indirect and accumulates error. The opticalposition sensor calibrates the electronic position monitoring and isparticularly useful for determining the slide position when there hasbeen a power outage or similar loss of machine control. In the recoveryphase, the presence or absence of an optical signal immediatelyindicates the direction of movement required to pass the centercalibration point. This optical sensor is presented in detail andpresents only one of many optical sensors used in the polishing systemof the invention to safeguard against overshoot and to enablerecalibration, especially in case of loss of power. Such sensors areattached to almost every movable part of the system whose absoluteposition is important.

As illustrated in perspective in FIG. 7 and in cross-section in FIG. 9,fixed to each of the four slides 908 is a respective wafer head assembly100, each including the wafer head 110, the wafer head motor 1012 and ahead rotation drive shaft 1014 with a surrounding non-rotating shafthousing 1015 connecting the two, as well as several other parts to bedescribed later. Each wafer head assembly 110 can be assembled away fromthe polishing apparatus 20, slid in its untightened state into the slot910 of the carousel support plate 906, between the arms of the slide908, and onto the rails 914, and there tightened to grasp the slide 908.

WAFER HEAD

Any of a number of different types of wafer heads can be used with theinvention, for example the one described by Shendon in U.S. Pat. No.5,205,082, incorporated herein by reference.

Diamond Wafer Head

Another exemplary head 110, schematically illustrated in cross sectionat the bottom of FIG. 9 and referred to generally as the diamond head,is the subject of U.S. patent application Ser. No. 08/549,474, filed onOct. 27, 1995 by Zuniga et al., incorporated herein by reference. Thishead 110 includes a downwardly facing bowl member 1110 of generallycylindrical form and a floater member 1112 generally fit within thecentral cavity of the bowl member 1110. The floater member 1112 includeson its lower side a wafer receiving recess 1115 surrounded by aretaining ring 1116 to define the recess 1114 into which the wafer 40 tobe polished is fit. The retaining ring 1116 may be fixed, asillustrated, to the floater member 1112 or may be flexibly connected tothe floater member 1112 or to the bowl member 1110 through an elasticconnection which tends to urge the retaining ring 1116 into contact withthe polishing surface of the polishing pad 54. The retaining ring 1116also prevents the wafer from sliding out sideways from under the waferhead 110 during polishing. In one configuration, a central shaft bushingassembly 1118 keeps the floater member 1112 in alignment with the bowlmember 1110. Misalignment of the wafer receiving portion and the rest ofthe head has been a problem in the past. A bushing 1120 fit into acentral aperture at the top of the floater member 1112 receives acentral shaft 1130 extending downwardly from the top of the bowl member1110 to thereby allow vertical movement between the bowl member 1110 andthe floater member 1112 while maintaining them in horizontal alignment.

A flexible seal connects the floater member 1112 to the bowl member 1110of the wafer head 110. Such a seal creates a fluid-tight cavity 1132 atthe back of the floater member 1112 while still allowing free relativevertical movement between the bowl and floater members 1110 and 1112.The seal may also be used to provide circumferential torque between thebowl and floater members 1110 and 1112 so as to keep them generallycircumferentially aligned. An example of a flexible seal is a rollingseal 1134 generally comprising an annular strip of elastomeric materialthat is sealed between the inside of the bowl member 1110 and thefloater member 1112 of the wafer head 110 as the bowl and floatermembers 1110 and 1112 move relative to each other. In this movement, theelastomeric strip of the rolling seal 1134 rolls over while maintaininga seal without interfering with adjacent pieces or adding a verticalforce component between the bowl and floater members 1110 and 1112.

3C Wafer Head

Yet another exemplary head 110', illustrated in cross section in FIGS.11 and 12 and referred to as the 3C head. Shendon et al. disclose such ahead in U.S. patent application, Ser. No. 08/488,921, filed Jun. 9,1995.

Referring now to FIG. 11, the internal structure of the 3C wafer head110' is shown in detail. Preferably, the head 110' includes a bowlmember 1160 having a downwardly facing recess 1162 therein, and withinwhich a carrier plate 1164 is received. To connect the head 110' to thehead drive shaft 1014, the bowl member 1160 includes an upwardlyextending, externally threaded, boss 1166 and the shaft 1014 terminatesagainst the raised boss 1166. A cup-shaped perimeter nut 1168, having adownwardly extending, internally threaded lip 1170 and a central recess1172 in the nut 1170 secures the head drive shaft 1014 to the bowlmember 1160. The end of the shaft 1014 extends through the nut recess1172, and a snap ring 1174 is placed into a snap ring bore locatedadjacent to the end of the shaft 1014 after the shaft end is extendedthrough the nut bore 1172. The snap ring 1174 prevents retraction of theshaft 1014 from the nut bore 1172. The cup-shaped perimeter nut 1168 isthen locked over the boss 1166 by threading the lip 1170 over theexternally threaded surface of the boss 1166, thereby trapping the snapring 1174 between the cup-shaped perimeter nut 1168 and the bowl member1160. To rotationally lock the head drive shaft 1014 and the bowl member1160, the shaft 1014 includes a keyway 1176 extending inwardly of itslower end, and the boss 1170 also includes a keyway 1178, which alignswith the shaft keyway 1176 when the shaft 1014 is received in theperimeter nut 1170. A key extends between the two keyways 1176 and 1178.Alternatively, a pin 1180 may be inserted into respective holes in theboss 1166 of the bowl member 1160 and the head drive shaft 1014.

The bowl member 1160 provides a substantially vertically fixed,rotationally movable, reference surface from which the substrate 40 isloaded against the polishing surface. In the preferred embodiment of theinvention as shown in FIG. 11, the substrate loading is accomplished byselectively positioning the carrier plate 1164 vertically with respectto the reference surface provided by the bowl member 1160 by means of aprimary, upper biasing chamber 1182 and a secondary, lower biasingchamber 1184. Preferably, the central recess 1162 is defined within theboundaries of the bowl member 1160, which in the preferred embodiment isa one-piece member, having an upper, horizontally extending plate-likeportion 1186 and a downwardly extending rim 1188. The carrier plate 1164is received within the recess 1162 and is extensible therefrom to locatea substrate received thereon against a polishing surface.

To enable selective positioning of the carrier plate 1164 in the recess1162, the primary biasing chamber 1182 includes a bellows 1190, whichextends between the underside of the upper plate 1186 and the uppersurface of the carrier plate 1164. These bellows 1190 are sealed attheir connection to the carrier plate 684 and the upper plate 1186 ofthe bowl member 1160, and these connections are also of sufficientstrength to support the mass of the carrier plate 1164 hanging from thebowl member 1160 without separation. Preferably, a bellows cavity 1192is formed within a removable bellows insert 1194, which includes anupper bellows plate 1196 and a lower bellows plate 1198 between whichthe bellows 1190 extend. The bellows 1190 are affixed to the plates 1196and 1198 to create the removable bellows insert 1194. To affix thebellows insert 1194 to the bowl member 1160 and to the carrier plate1164, a plurality of unillustrated bolts extend through the rim of thelower bellows plate 1198 and into the top of the carrier plate 1164, anda plurality of unillustrated bolts extend through the plate-like portionof the bowl member 1160 and into threaded holes in the upper bellowsplate 1196.

The secondary loading assembly 1184 of the wafer head 110' includes abow chamber 9102 which is formed within the carrier plate 684. The bowchamber 9102 is a sealable cavity having a thin, generally planarmembrane 9104 against which a conformable material 9106, such as a pieceof polishing pad material, may be located to form a conformablesubstrate receiving surface for the surface of the wafer.

To polish a substrate using the head 110', a substrate is loaded againstthe material 9106 covering the planar lower surface of the membrane9104. The head 110' is then positioned over one of the polishing pads54, and the bellows cavity 1192 is pressurized to enlarge itself tothereby bias the carrier plate 1164 toward the polishing surface andthereby load the substrate against it. To vary the pressure between thecenter and the edge of the substrate, the bow chamber 9102 ispneumatically pressurized. The positive pressure will bend the planarmembrane 9104 outwardly, and the center of the planar surface willextend furthest outwardly in a convex structure to increase the loadingbetween the substrate and the polishing surface near the center of thesubstrate. Negative pneumatic pressure, on the other hand, tends tocreate a concave structure.

Referring still to FIG. 11, the head 110' also preferably includes aretainer ring 9110, which, during polishing, extends into contact withthe polishing surface and which is otherwise retractable inwardly andupwardly of the head 110'. In this embodiment of the head 110', the ring9110 is an annular member having a planar base 9112 on which areplaceable contact ring 9114 is fixed, and it further includes anoutwardly extending annular ledge portion 9116. The bowl member 1160includes an inwardly extending annular ledge 9118, which extends belowthe surface of the outwardly extending ledge portion 9116 of theretainer ring 9110. To secure the retainer ring 9110 within the recess1162 of the bowl member 1160, a plurality of compressed springs 9120extend between the inwardly extending ledge 9118 and the underside ofthe outwardly extending ledge 9116. These springs continuously bias theretainer ring 9110 inwardly and upwardly of the bowl member 1160. Toproject the retainer ring 9110 downwardly out of the bowl member 1160,and to vary and control the extent of projection, an inflatable toroidalbladder 9122 extends between the upper surface of the outwardlyextending ledge 9116 of the retainer ring 9110 and the underside of amiddle ledge 9124 of the bowl member 1160 about the entire circumferenceof the retainer ring 9110. When the bladder 9122 is evacuated, as shownin FIG. 8, through structure similar to a stem on a tire tube, theretainer ring 9110 is retracted inwardly and upwardly of the head 110'.When the bladder 1188 is positively pressurized, the bottom of theretainer ring 9110 extends downwardly from the head 110', as shown inFIG. 12. The bladder 1188 may be replaced by two annular bellows ofeither rubber or metal defining an annular cavity between them.

FIG. 11 additionally shows vertical passages 9130, 9132, 9134, 9136, and9138 extending along the drive shaft 1014 and sealed to various passagesin the head 110' to selectively supply vacuum, pneumatic pressure orfluid to elements of the head. The vertical passage 9130 connects viaside passage 9140 and vertical passage 9142 to the bladder 9122. Thevertical passage 9132 connects via side passage 9144 to the area betweenthe bellows insert 1182 and the retaining ring 9110. The verticalpassage 9134 connects via passage 9146 to the bellows cavity 1192. Thevertical passage 9136 connects via passage 9148 to the bow chamber 9102.The vertical passage 938 connects via side passage 9150 and verticalpassage 9152 to a port 9154 at the bottom surface 9106 of the membrane9104 so as to selectively hold and eject wafers in and from the head110'.

3C3 Wafer Head

FIG. 12A shows an alternate embodiment of a wafer head 110", referred tothe 3C3 head, which is a modification of the 3C wafer head 110' of FIGS.11 and 12. The 3C3 wafer head 110" comprises three major assemblies: abase assembly 9202, a housing assembly 9204, and a retaining ringassembly 9206. A bellows system 9208 is positioned between the housingassembly 9204 and the base and retaining ring assemblies 9202 and 9206.Each of these assemblies is explained in detail below.

The base assembly 9202 applies a load to the wafer 40; that is, itpushes the wafer 40 against the polishing pad 54. The base assembly 9202can move vertically with respect to housing assembly 9204 to carry thewafer to and from the polishing pad. The bellows system 9208 connectsthe housing assembly 9204 to the base assembly 9202 to create an annularprimary pressure chamber 9210 therebetween. Fluid, preferably air, ispumped into and out of the primary pressure chamber 9210 to control theload on the wafer 40. When air is pumped into the primary pressurechamber 9210, the pressure in the chamber increases and the baseassembly 9202 is pushed downwardly.

The bellows system 9208 also connects the housing assembly 9204 to theretaining ring assembly 9206 to create an annular secondary pressurechamber 9212. Fluid, preferably air, is pumped into and out of thesecondary pressure chamber 9212 to control the load on the retainingring assembly 9206.

As explained below, the housing assembly 9204 is connected to androtated by the drive shaft 1084. When the housing assembly 9204 rotates,the bellows system 9208 transfers torque from the housing assembly 9204to the base assembly 9202 and the retaining ring assembly 9206 andcauses them to rotate.

The base assembly 9202 includes a disk-shaped carrier base 9214 having anearly flat bottom surface 9216 which may contact the wafer 40. A topsurface of the carrier base 9214 710 includes a centrally locatedcircular depression 9220 surrounded by a generally flat annular area9222. The annular area 9222 is itself surrounded by a rim 9224. Severalvertical conduits 9226, evenly spaced about a central axis 9228 of thewafer head 110", extend through the carrier base 9214 from the bottomsurface 9216 to the central circular depression 9220.

A generally flat annular plate 9230 rests primarily on the annular area9222 of the carrier base 9214, with the outer edge of the annular plate9230 abutting the rim 9224 of the carrier base 9214. An inner portion9232 of the annular plate 9230 projects over the central circulardepression 9220. The annular plate 9230 may be attached to the carrierbase 9214 by bolts 9234 which extend through passages in the annularplate 9230 and engage threaded recesses in the carrier base 9214.

A stop cylinder 9240 is mounted in a central opening 9238 in the annularplate 9230. The stop cylinder 9240 includes a tubular body 9242, aradially outwardly projecting lower flange 9244, and a radiallyoutwardly projecting upper flange 9246. The lower flange 9244 engages alip 9248 at the inner edge of the annular plate 9230 to support the stopcylinder 9240 above the annular plate 9230. The gap between the lowerflange 9244 of the stop cylinder 9240, the circular central depression9216 of the carrier base 9210, and the inner portion 9232 of the annularplate 9230 creates a central cavity 9250 in the base assembly 9202. Acentral channel 9252 extends vertically through the tubular body 9242from the lower flange 9244 to the upper flange 9246 to provide accessfor fluid to the central cavity 9250 and the vertical conduits 9226.

The housing assembly 9204 includes at its top a disk-shaped carrierhousing 9260. The bottom surface of the carrier housing 9260 has acylindrical cavity 9262. The bottom surface also has an inner annularsurface 9264 and an outer annular surface 9266 which may be separated bya downwardly projecting ridge 9268. The top surface of the carrierhousing 9260 includes a cylindrical hub 9270 with a threaded neck 9274which projects above an upwardly facing middle annular area 9272. Agently sloped section 9276 surrounds the middle annular area 9272, and aledge 9278 surrounds the sloped section 9276.

The housing assembly 9204 also includes below the carrier housing 9260an annular inner plate 9280 and an annular outer plate 9282. The innerplate 9280 is mounted to the inner annular surface 9264 on the bottom ofthe carrier housing 9260 by a set of bolts 9284, and the outer plate9282 is mounted to the outer annular surface 9266 by another set ofbolts 9286. The outer edge of the inner plate 9280 abuts the ridge 9268in the carrier housing 9260. The inner edge of the inner plate 9280projects horizontally under the cylindrical cavity 9262 to form aninwardly pointing lip 9290 surrounding an opening 9292 between it andthe stop cylinder 9240. The top of the cylindrical cavity 9262 is closedby a ceiling 9294. The stop cylinder 9240 of the base assembly 9202extends through the opening 9292 into the cylindrical cavity 9262, andits upper flange 9246 projects horizontally over the lip 9290.

There are several conduits in the housing assembly 9204 to provide forfluid flow into and out of the wafer head 110". A first conduit 9300extends from the bottom surface of the inner plate 9280, through thecarrier housing 9260, and (in an unillustrated passage) to top of thehub 9270. A second conduit 9302 extends from the cylindrical cavity 762through the carrier housing 9260 to the top of the hub 9270. A thirdconduit 9304 extends from the bottom surface of the outer plate 9282through the carrier housing 9260 to the top of the hub 9270. O-rings9306 inset into the top and bottom surfaces of the hub 9270 surroundseach conduit so as to seal them against adjoining members.

The wafer head 110" may be attached to the drive shaft 1084 by placingtwo dowel pins (not shown) into dowel pin holes (not shown) and liftingthe wafer head so that the dowel pins fit into paired dowel pin holes(not shown) in a drive shaft flange 1084a. This aligns angled passagesin the drive shaft 1084 to the conduits 9300, 9302 and 9304. Then thethreaded perimeter nut 1068 can be screwed onto the threaded neck 9274to attach the wafer head 110" firmly to the drive shaft 1084.

The bellows system 9208 includes several cylindrical metal bellowsdisposed concentrically in the space between the base assembly 9202 andthe housing assembly 9204. Each bellows can expand and contractvertically. An inner bellows 9310 connects the inner edge of the innerplate 9280 to the lower flange 9244 of the stop cylinder 9240 to sealthe upper central cavity 9262 and the central channel 9252 from theprimary pressure chamber 9210. A pump (not shown) can pump air into orout of the vertical conduits 9226 via the second conduit 9302, the uppercentral cavity 9262, the central channel 9252, and the lower centralcavity 9250 to vacuum-chuck or pressure-eject the wafer to or from thebottom surface of the wafer head 110".

An outer bellows 9312 connects the outer edge of the inner plate 9280 tothe annular plate 9230. The ring-shaped space between the concentricinner bellows 9310 and outer bellows 9312 forms the primary pressurechamber 9210. A pump (not shown) can pump air into or out of the primarypressure chamber 9210 via the first conduit 9300 to adjust the pressurein the primary pressure chamber 9210 and thus the load that the head110" exerts on the wafer 40.

When the primary pressure chamber 9210 expands and the base assembly9202 moves downwardly with respect to the housing assembly 9204, themetal bellows 9310 and 9312 stretch to accommodate the increaseddistance between the annular plate 9230 and the inner plate 9280.However, the flange 9246 of the stop cylinder 9240 will catch againstthe lip 9290 of the housing assembly 9204 to stop the downward motion ofthe base assembly and prevent the bellows from over-extending andbecoming damaged.

The retaining ring assembly 9206 includes an L-shaped ring support 9320with a inwardly directed horizontal arm 9322 and an upwardly directedvertical arm 9324. A backing ring 9330 is attached to the top of thehorizontal arm 9322 by bolts 9332. An outer portion 9333 of the backingring 9330 abuts the vertical arm 9324 of the L-shaped ring support 9320,and an inner portion 9334 of the backing ring 9330 may projecthorizontally over the rim 9224 of the carrier base 9214. A flexible seal9335 connects the retaining ring assembly 9306 to the carrier base 9214to protect the wafer head from slurry. The outer edge of the seal 9335is pinched between the backing ring 9330 and the horizontal arm 9322 ofthe L-shaped ring support 9320, whereas the inner edge of the seal 9335is attached by an adhesive to the carrier base 9214. A verticallyextending flange 9336 is attached to the outside of the vertical arm9324 of the L-shaped ring support 9320 and forms the outer wall of thewafer head 110". The flange 9336 extends upwardly to almost touch thecarrier housing 9260. A seal 9338 rests on the ledge 9278 of the carrierhousing 9260 and extends over the vertically extending flange 9336 toprotect the wafer head 110" from contamination by slurry. A retainingring 9340 is mounted to the bottom surface of the horizontal arm 822 ofthe L-shaped ring support 9320 by unillustrated recessed bolts. Theretaining ring 9340 includes a inner, downwardly protruding portion 9342which will contact the polishing pad 54 and block the wafer 40 fromslipping out from under the base assembly 9202.

A third cylindrical bellows 9314 connects the inner edge of the outerplate 9282 of the housing assembly 9302 to the inner portion 9333 of thebacking ring 9330. A fourth cylindrical bellows 9316 connects the outeredge of the outer plate 9282 to the outer portion 933 of the backingring 9330. The ring-shaped space between the concentric third and fourthbellows 9314 and 9316 forms the secondary pressure chamber 9212. A pump(not shown) can pump air into or out of secondary pressure chamber 9212via the third conduit 9304 to adjust the pressure in the secondarypressure chamber 9212 and thus the downward pressure on retaining ring9340. Because the primary and secondary chambers 9210 and 9212 arepressurized independently, the base assembly and retaining ring can beindependently actuated in the vertical direction.

Wafer Head Mounting

Referring now additionally to the enlarged cross section of FIG. 10 withparticular reference to the diamond wafer head 110 of FIG. 9 althoughlarge parts of the discussion are also applicable to the 3C wafer head110' of FIG. 11 and the 3C3 wafer head 110 of FIG. 12A, the verticalpolishing force to polish the wafer is supplied by pressurized fluidrouted to the fluid-tight cavity 1132 between the bowl and floatermembers 1110 and 1112. The pressurized fluid, which may be air or water,is supplied to the wafer head 110 though a first axial channel 1040 (oneof four such channels) in the head drive shaft 1014. A rotary coupling1042 (to be described later) at the top of the shaft above the rotarymotor 1012 couples four fluid lines into the shaft channels of therotating shaft 1014. A first angled passageway 1044 formed in a shaftflange 1046 of the head drive shaft 1014 connects the first shaftchannel 1040 to a vertical passageway 1048 in a top hub 1150 of thedownwardly facing bowl member 1110. The vertical passageway 1148 extendsdown to the fluid-tight cavity between the bowl and floater members 1110and 1112 to control the pressure therein. A similar angled passageway1052 and vertical passageway 1054 connect a second shaft channel 1056 tothe interior of the wafer head 110, and like elements are provided forthe remaining two shaft channels if desired. Plugs 1058 are placed atthe bottom of the bored shaft channels 1040 and 1056 to seal them. Sealsare placed between the respective angled passageways 1044 and 1052 inthe shaft flange 1046 and the vertical passageways 1044 and 1052 in thebowl member 1110 to confine the fluids contained therein.

When the drive shaft 1014 and the wafer head 110 are placed together,two dowel pins 1060 are placed in paired dowel holes 1062 and 1064 inthe bowl hub 1050 and the shaft flange 1046 to circumferentially alignthe shaft 1014 and bowl member 1110, particularly their fluid passages.A perimeter 1066 of the bowl hub 1050 is threaded, and a perimeter nut1068 is screwed thereon. The perimeter nut 1068 has a lip 1070 that issmaller than the outside diameter of the shaft flange 1046 and fits overthe top of the flange 1046 of the drive shaft 1014 to thereby clamp andhold the drive shaft 1014 to the bowl member 1110 of the wafer head 110.

The separate fluid connections can be used for a number of purposes. Forexample, the passages can be utilized (1), to route a vacuum orpressurized gas source to the recess 1115 where the wafer is broughtinto contact with the wafer head 110 (this is the configuration on theright side of FIG. 9 which requires a sliding seal 1072 through thefluid-tight cavity 1132 to a vertical passageway 1074); (2), to route avacuum or pressurized gas source to the bowl member 1110 of the waferhead 110 to control the vertical extension and retraction of the floatermember 1112 of the wafer head 110 from the bowl member 1110 (this is theconfiguration of both heads 110 and 110'); (3), to use two passages (asupply and return) to circulate cooling water through the wafer head 110to control the wafer temperature; and (4), if the rotary coupling 1042permits it, to route electrical lines through the channels, e.g., tomeasure a temperature of the wafer head 110.

The lower floater member 1112 of the wafer head 110 moves verticallyrelative to the upper fixed bowl member 1110 based upon the fluidpressure supplied to the sealed cavity 1132 between the former members1110 and 1112. Air pressure supplied behind the rolling seal 1034between the floater member 1112 and the bowl member 1110 causes thefloater member 1112 to descend to contact the polishing pad 54 forpolishing the wafer 40 mounted in the recess 1115 of the floater member1112. Similarly, when it is desired to raise the wafer 40 to move it tothe next polishing station or transfer station, vacuum is supplied tothe sealed cavity 1132 to cause the floater member 1112 holding thewafer 40 to rise.

As illustrated, the stroke of the floater member 1112 within the bowlmember 1110 is very small, of the order of 0.2 inches (5 mm), and thisis the only vertical motion of either the wafer head systems 100, thecarousel 90, or the polishing stations 50. Such a short stroke is easilyaccommodated within the lower end of the wafer head and can be achievedpneumatically. The short stroke is a major factor is simplifying thedesign and reducing the cost of manufacturing and operating thepolishing system of the invention.

Head Shield Plates

The overall design of the wafer head system 100 requires that it passthrough the slot 910 of the carousel support plate 906 and radiallyoscillate within that slot 910. Chemical mechanically polishing is a wetand particle-intense operation. The wafer head 110 and associatedelements have been carefully designed to exclude the polishingenvironment from the interior of the head 110. The linear bearing railassemblies 912 and motors 1012 and other equipment above the carouselsupport plate 906 are sensitive to moisture and grit, and it would bepreferable to design a seal about the point where the wafer headassembly 100 passes through the carousel support plate 906 that wouldprevent the polishing environment from substantially penetrating pastit. The splash plate assembly to be described now performs thatfunction.

As best shown generally in perspective in FIG. 7, a splash plateassembly 940 is attached to the underside of the carousel support plate906. The splash plate assembly 940 prevents polishing slurry, which isabrasive, chemically active, and tends to coat everything in itsvicinity with a thin layer of slurry and/or alkaline residue, fromgetting up into the upper portion of the multi-head carousel assembly 90and creating undesired effects (such as shorting of electricalconnections and contamination of exposed sliding and rolling metalsurfaces). The splash plate assembly 940 includes a series of movingslot covers which are configured to provide a slot splash-guard closurewithin the range of radial oscillation of the wafer head system 100. Theclosure is accomplished with a horizontal projection that provides asplash shield for the slot without a horizontal projection substantiallylonger than the length of oscillation in the slot.

The splash plate assembly 940 attached to the underside of the carouselsupport plate 906 includes a central shield plate 942 that can bescrewed to the bottom side of carousel support plate 906 prior to itsassembly on the center post 902. The carousel support plate 906 furtherincludes four outer shield plates 944 which can also be screwed to thebottom of the carousel support plate 906 in butted sealing juxtapositionto the central shield plate 942 when the wafer head systems 100 arebeing fit into the carousel support plate 906. Both the central andouter shield plates 942 and 944 form a rectangular, round-cornered,elongate recess 946 offset from the centerline of each slot's radialaxis. An elongated, round-cornered splash slot 948 is formed in both thecentral and outer shield plates 942 and 944 at their junction. As bestshown in the cross section of FIG. 10, both the central and outer shieldplates 942 and 944 are formed with an upwardly extending flange 950facing and surrounding the splash slot 948. As shown in the plan viewsof FIGS. 14A through 14C, the linear axis of the splash slot 948generally follows the axis of the corresponding slot 910 in the carouselsupport plate 906. The rounded portions of the splash slot 948 have aninner diameter substantially larger than the outer diameter of thenon-rotating drive shaft housing 1015 that passes therethrough, and thelinear portion has a length generally matching the distance of theradial oscillation range of each wafer head system 100.

As best shown in perspective in FIG. 7, a D-shaped splash follower 952has one convexly curved edge and a second substantially straight or lesscurved edge smoothly joined to each other. The splash follower 952includes a circular hole 954 disposed near its curved edge. The driveshaft housing 1015 is rotatably fitted in this hole 954, as will bedescribed shortly, to allow the D-shaped splash follower plate 952 torotate as the wafer head 110 and attached drive shaft housing 1015oscillate along the slot 910 of the carousel support plate 906. EachD-shaped plate 952, as best shown in the cross section of FIG. 10, has adownwardly facing flange 956 along the entirety of its outsideperimeter. The flanges 950 and 956 of the central and outer splashplates 942 and 944 and of the splash follower 952 are generally of thesame length and facing respectively up and down at the edges of thestationary and moving shield pieces. When assembled, the flanges 950 and956 and the flat bottoms of the opposed pieces 942, 944, and 952 areseparated by gaps of about 0.064" (2.15 mm). The flanges 950 and 956thus create a generally tortuous labyrinthine path to prevent slurrysplashed toward the slots 910 from passing from the slurry side of thecarousel support plate 906 through the slots 910 and into the motors andbearings located inside the carrier assembly cover 908.

As best shown in the cross section of FIG. 10, each D-shaped splashplate 952 is rotatably fixed to a splash flange 960 formed on theoutside of the shaft housing 1015. A perimeter skirt 962 is fitted tothe lower end of the drive shaft housing 1015 and has an upwardlyextending portion 964 including a ledge 966 which presses the internalrace of a splash shield bearing 968 against the splash flange 960 of thedrive shaft housing 1015. The outside race of the bearing 968 is clampedtightly from the bottom by an inwardly extending flange 970 of theD-shaped splash follower 952 and from the top by a collar assembly 972of two or more pieces and by screws 974 which clamp the bearing 968 tothe flange 970 of the splash follower 952. The collar 972 overlaps, butdoes not touch the top of the splash shield flange 960 on the shafthousing 1015.

The D-shaped splash follower 952 is attached to the bearing 968 to bethereby held firmly, but rotates freely relative to the shaft housing1015. The D-shaped splash follower 952 has a vertical (pivot) pin 976fixed to its top. This vertical pin 976 has a roller bearing 978attached to its upper end that is guided within a horizontal guidegroove 980 formed in the bottom of the carousel support plate 906. Asshown in the perspective view of FIG. 8 and in the plan views of FIGS.14A through 14C, the pivot pin 976 is disposed on the medial line ofsplash follower 952 between the circular hole 954 and the flat edge ofthe D-shaped splash follower 952. The outside of the roller bearing 978rides in the horizontal guide groove 980 on the bottom of the carouselsupport plate 906, which extends to or almost to the radial slot 910 inthe carousel support plate 906 but is angularly offset from it.Preferably, the guide groove 980 is perpendicular to the radial slot910.

As the shaft 1014 and shaft housing 1015 radially oscillate in thecarousel support plate 906 to move the wafer head 110, the center hole954 of the splash follower 952 follows the shaft housing 1015. Thismotion also moves the pivot pin 976 on the splash follower 952 whosedirection of motion is restricted to the perpendicular direction as itfollows the guide groove 980 in the carousel support plate 906. Thesplash follower 952 is thereby caused to rotate as it is held inalignment between the shaft housing 1015 and the pivot pin 976. Theoscillatory motion of the shaft housing 1015 thus causes a correspondingoscillatory and partially orbital motion in the D-shaped splash follower952.

The motion of the D-shaped shield plate 688 can be seen in the top viewsof FIGS. 14A, 14B, and 14C. As the wafer head 110 moves from aninnermost position to an outermost position along the slot 910 of thecarousel support plate 906, that is, as the drive shaft housing 1015moves along the slot 910, the guide groove 980 constrains the pivot pinto move perpendicularly to the slot 910 and to thus cause the splashfollower 952 to partially orbit the drive shaft housing 1015 as itfollows it in the slot direction.

The D-shaped splash follower 952 orbits as it is constrained between twopoints, the central axis of the drive shaft housing 1015 and the centralaxis of the vertical pivot pin 978. As the drive shaft housing 1015oscillates, the D-shaped splash follower moves with the drive shafthousing 1015. The pivot pin 976 also moves under the influence of thedrive shaft housing 1015, but instead of moving radially in the radialslot 910, as does the drive shaft housing 1015, it moves in theperpendicular guide groove 980 of the carousel support plate 906. Sincethe splash follower 952 is connected to the drive shaft housing 1015through a ball bearing 968 and the pivot pin 976 of the splash follower952 is connected the guide groove 964 of the carousel support plate 906through a roller bearing 978, there is no sliding contact between pieceswhich could generate metal particles which could fall on wafers beingpolished and damage them. In all positions, the slot 910 is covered bythe orbiting splash follower 952 and direct splashing of the slurrythrough the slot is prevented. Nonetheless, the splash follower 952 hasan operating span that is less than if it did not orbit about the driveshaft housing 1014.

The motion of the splash plate assembly 940 and particularly the motionof the D-shaped splash follower 952 are shown in three longitudinalcross-sectional views of FIGS. 15A, 15B, and 15C taken along the axis ofthe slot 910 of the carousel support plate 906, in three axialcross-sectional views of FIGS. 16A, 16B, and 16C, and in threeperspective views of FIGS. 17A, 17B, and 17C. Like-lettered figures inthese three sets correspond to the plans views of FIGS. 14A, 14B, and14C, respectively. In the perspective views, the pivot pins 976 on thetop of the splash follower 952 is shown engaging the guide groove 980 ofthe otherwise unillustrated carousel support plate 906.

FIGS. 10A, 10B, and 10C clearly show the pivot pin 976 moving from aninward position, to an outward position, and again to the inwardposition within the guide groove 980 as the drive shaft housing 1015moves from the radially innermost position of FIG. 16A, to a medianposition of FIG. 16B, to a radially outermost position of FIG. 16C.Especially, FIGS. 16A, 16B, and 16C show that the splash follower 952always covers the closed slot 948 formed in the central and outer splashplates 942 and 944 which is the principal path from the polishing areato the back of the carousel support plate 906. The plan views of FIGS.14A, 14B, and 14C and the perspective views of FIGS. 17A, 17B, and 17Cshow that the closed slot 948 is covered by a mechanism that takes up aminimum of radial space along the central and outer splash plates 942and 944 and thus along the radial slot 910 of the carousel supportplate. Thereby, the size of the mechanism is reduced with anaccompanying reduction in the footprint of the polishing system.

Both sets of side-view figures shows that the flange 950 extendingupwardly from the central and outer splash plates 942 and 944 and theflange 956 extending downwardly from the splash follower 952 alwayscreate a labyrinthine path for moisture and particles attempting topenetrate to the back of the carousel support plate 906.

Rotary Union

The rotary union 1042 of FIG. 9 can be achieved by commerciallyavailable units. However, a preferable, novel rotary union 2100 isillustrated in cross section in FIG. 13. The spindle shaft 1014 abovethe wafer head motor 1012 contains four vertical channels, only two suchchannels 1040 and 1056 being illustrated. At its upper end, above therotary motor 1012, it is joined to a spindle 2114 having four similarvertical passages 2116 aligned to those of the spindle shaft 1014 by adowel 2118 at the lower end of the spindle 2114 and sealed thereto byunillustrated O-rings in recesses 2120. A quick-disconnect clamp 2122joins the spindle 2114 to the spindle shaft 1014. Both the spindle shaft1014 and the spindle 2114 are rotating with the wafer head 110. Aanti-rotation plate 2134, on the other hand, is fixed to some point onthe assembly, such as the casing of the wafer head motor 1012.

A rotary assembly 2140 comprises four vertically stacked and separablesections 2142a, 2142b, 2142c, and 2142d, principally composed ofrespective annular rotary members 2143a, 2143b, 2143c, and 2143d. Eachrotary member 2143a through 2143d includes a tapped hole 2144 to bethreaded with a male threaded end of a detachable connector for a fluidline or other line. This design is easily integrated with a sectionproviding one or more electrical connections down through the spindle2114 in which a radial spring-loaded contact slides on a circumferentialcommutator rotating on the spindle 2114. Each tapped hole 2144 isconnected by a radial passageway 2146 to an annular manifold 2148surrounding the spinning spindle 2114. The rotary seal between thesections 2142a-2142d and the spindle 1014 is accomplished by flangetshaft seals 2150. Each such flanget shaft seal 2150 is an annularelastic U-shaped member 2150, with the bottom of the U oriented awayfrom the center of the annular manifold 2148 and having substantiallyflat sides sealing the sides of the spindle 2114 against respective onesof the rotary members 2143. Each lip seal 2150 has a tail 2149 extendingradially outwardly. The outer surface of each lip seals 2150 is composedof a moderately hard elastomeric material. Each lip seal 2150 includeswithin its U-shaped cavity an annular spring member joined along itsradially innermost portion within the U and having fingers extendingdown the inner wall toward the bottom of the U and then upwardly alongthe outer wall so as to force the two walls apart to seal the rotarymembers 2143 relatively rotating about the spindle 2114. An example ofsuch a flanglet seal is Model W30LS-211-W42, available from Variseal.

The two lip seals 2150 are fit into the sides of the annular manifold2148. However, such lip seals 2150 work best only if their interiorsides have positive pressure with respect to the pressure outside thebottom of the U. But, it is desired that at least the middle two of thefour lines have a negative pressure, that is, less than atmosphericpressure, applied through them for at least some of the time.Accordingly, a male connection of a detachable connector of a vacuumline is threaded into a tapped vacuum hole 2151 in one central rotarymember 2142b. The bottom of the vacuum hole 2151 connects to a verticalvacuum passage 2152 bored in the center ones of the rotary members 2142band 2142c. The vertical vacuum passages 2152 connect to threeinter-sectional manifolds 2148 formed between the four rotary members2142. A stainless-steel washer 2156 fits within a recess of the rotarymembers 2142 and fills the inner portion of each inter-sectionalmanifold 2154 up to but not quite touching the rotating spindle 2130 andsupports the back of the lip seals 2150. The washers 2156 trap the tails2149 of the lip seals 2151 against the rotary members 2142. Separateelements perform similar trapping at the very top and bottom. Eachwasher 2156 has four radial grooves formed in each principal surface soas to distribute the vacuum to the back of each adjacent lip seal 2150.As a result, regardless of the pressure applied through the tapped holes2144 to the respective manifolds 2148, a positive pressure is alwaysmaintained from the interior of the lip seal 2150 and its outside. Itshould be mentioned that the top and bottom sections 2042d and 2042ahave not been designed for a negative pressure. Therefore, the uppermostand bottommost lip seal 2150 are not provided with backside vacuum.

As shown in FIG. 13, each of the stationary rotary members 2143a through2143d is connected to a respective one of the vertical passages 2116 inthe rotating spindle 2114 via a side passage 2160 bored radially in thespindle 2114 at the proper height for that section. Each side passage2160 is continuously connected to its associated annular manifold 2148.

An upper flange 2180 is placed over the uppermost rotary member 2143dand four bolts 2182 pass through a respective through hole 2184 alignedwith through holes 2162 of the upper three rotary members 2143b, 2143c,and 2143d and are screwed into the tapped hole 2164 of the bottom rotarymember 2143a. O-rings 2166 are placed between neighboring sections toensure fluid sealing.

The lower rotary member 2143a includes at least one tapped hole 2168 forrespective bolts fixing the rotary union 2100 to the spatially fixedanti-rotation plate 2134. It further includes an inner, lower recess fora collar 2172 pressing the outer race of a lower ring bearing 2170against a ledge 2176 in the anti-rotation plate 2134. The inner race ofthe lower ring bearing 2170 is held on its lower side by a ledge 2178 inthe spindle 2114 but floats on its upper end.

The rotary assembly 2140 is placed over the spindle 2114 with the lowerring bearing 2170 at the bottom and an upper ring bearing 2186 placed onupper ledges of the spindle 2114 and the upper flange 2180. The outerrace of the upper ring bearing 2186 is held by a bearing flange 2187fixed by screws 2188 to the upper flange 2180. The inner race of theupper ring bearing 2186 is biased toward the ledge of the spindle 2114by an O-ring 2189 pressured by a wave spring 2190 pressed downward by atop flange 2192 secured to the top of the spindle 2114 by screws 2194.

This rotary coupling is particularly advantageous in that its totalheight above the drive shaft is 10.4 cm (4.08 inches), that is, 2.6 cmper section. The simple design also minimizes the lateral dimension andthe total weight. All these factors contribute to a polishing apparatusand particular wafer head systems that are compact.

Of course, the invention of the rotary union is not limited to the foursections. It is applicable to a single rotary feedthrough, but it ismost advantageous to two or more rotary feedthroughs.

Assembly of the Wafer Head Assembly

The principal parts of the wafer head system 100 have already beendescribed. This section will describe a few final parts necessary tojoin it to the other parts and to provide proper sealing and bearingsurfaces, as required.

The wafer head system 100 is shown in the complete cross section of FIG.9 and the partial enlarged cross section of FIG. 10. The drive shafthousing 1015 holds the shaft 1014 by paired sets of lower ring bearings1080 and an upper ring bearing 1082. The outer race of the lower ringbearings 1080 are held in an inside counterbore 1084 at the bottom endof the drive shaft housing 1015 by a notched retainer rim 1086 tightenedagainst the drive shaft housing 1015 by a set of screws 1088. Theretainer rim 1086 also supports and clamps the ascending portion 964 ofthe perimeter skirt 962 against the splash bearings 968 so as to affixthe inner race of the splash bearings 968 to the drive shaft housing1015. The offset of the collar from the bearing provides a small degreeof elastic compliance to allow for dimensional differences due tomanufacturing.

The inner race of the lower ring bearing 1080 rests on a shoulder 1090near the bottom of the spindle shaft 1014. A shaft bushing 1092 isloosely fitted between the spindle shaft 1014 and drive shaft housing1015 and acts as a collar clamping and separating the inner races of thelower and upper ring bearings 1080 and 1082 while the outer races areheld by the drive shaft housing 1015. A pair of retaining nuts 1094 arethreaded onto the upper portion of the spindle shaft 1014 to hold andlock the inner races of the rings bearings 1080 and 1082 to the spindleshaft 1014. The outer race of the upper bearing 1082 is also locked tothe top of the shaft housing 1015, as the tightening of the nuts 1094tends to clamp the bearings 1080, 1082 to the shaft housing 1015. Thespindle shaft 1014 passes upwardly through the hollow shaft of the waferrotation motor 1012. The upper end of the spindle shaft 1014 above themotor 1012 is held by a clamp collar 1095 that is attached to the rotorof the motor 1012. A motor bracket 1096 is connected to the upper end ofthe drive shaft housing 1014 below the motor 1012 to support the motor1012 on the shaft housing 1015, and a lip 1098 depending from thebracket 1096 positions the bracket 1096 to the drive shaft housing 1015.

The wafer head system 100 can be assembled while removed from thecarousel 90, with the exception of the outer splash plates 944 and aloosened central splash plate 942, and then the nearly complete assemblyis inserted into the slot 910 of the carousel support plate 906. Anupper flange 1100 of the drive shaft housing 1015 fits onto ledges 1102formed on the inner sides of the arms of the slide 908 and a set ofbolts 1104 fasten the upper flange 1100 and thus the drive shaft housing1015 to the slide 908. This simple mating between the wafer head system100 and the carousel 90 significantly reduces downtime when a wafer headneeds to be replaced.

Table Top Layout

FIG. 18 shows a top plan view (with the exception of the center post802) of the table top 23 of the machine base 22. As described before,the three polishing stations 50a, 50b, and 50c and the transfer station70 are arranged in a square configuration on top of the machine base.Each polishing station includes the respective rotatable platen 52overlaid with the polishing pad 54, where the polishing pads 54 for thedifferent polishing stations may have different characteristics. Thefirst elongate intermediate washing station 80a is located between thefirst two polishing stations 50a and 50b, and the second intermediatewashing station 80b is located between the second two polishing stations50b and 50c. A third washing station 80c is located between the thirdpolishing station 50 and the transfer station 70, and optionally afourth washing station 80aa may be located between the transfer station70 and the first polishing station 50a. These serve to wash slurry fromthe wafer as it passes from one polishing station to the next.

Associated with each polishing station is the respective conditionerapparatus 60a, 60b, or 60c, each including its pivotable arm 62 holdingits conditioner head 64 on its distal end and further including itsconditioner storage cup 68 for storing the conditioner head 64 when it'snot in use. Although the detailed embodiments describe a disk-shapedrotating conditioner head, the conditioner head could be a wheel or rod.FIG. 18 shows the storage cups 68 of the first and second polishingstations 50a and 50b being in an inactive position outboard of the sweeppath of the conditioner arm 62 with the conditioner head 64 positionedover the pad 54, which it reconditions as the rotatable arm 62 sweepsacross the pad. On the other hand, this figure shows the storage cup 68of the third polishing station 50c being swung from its inactiveposition 68' (shown in dashed lines) to a storage position 68" inboardof the conditioner arm 62 so that the conditioner head 64 can be storedtherein when the conditioning arm 62 is idle.

The structural details and operation of these various parts will now bedescribed in separate sections.

Platen Assembly

A platen assembly 500, shown in the cross-sectional view of FIG. 19, isreplicated at every polishing station 50a, 50b, and 50c. The platen 52includes a platen top 510 and a platen base 512 joined to it by severalperipheral screws 513 countersunk into the bottom of the platen base512. For polishing of 8-inch (200 mm) wafers, the platen 52 may have adiameter of 20 inches (51 cm). The bottom of the platen 52 includes adownwardly projecting, wedge-sectioned rim 514 that rotates within acorresponding annular drain channel 515 formed in the table top 23leaving only a narrow, winding passage therebetween 523 for slurry topenetrate towards the bearings.

A collar 516 at the bottom of the platen base 512 captures the innerrace of a platen ring bearing 518 and presses it against a flatcylindrical cornice 519 formed on the lower side of the platen base 512.A set of screws 520 countersunk into the bottom of the collar 516 arethreaded into the bottom of the platen base 52 and clamp the collar 516to hold the inner race. Another collar 522 supported on the table top 23and protruding upwardly into an annular cavity on the outer, lowerportion of the platen base 512 captures the outer race of the platenring bearing 516 against a ledge 222 formed in the table top 23 of themachine base 22. A set of screws 524 countersunk into the bottom of thetable top 23 are threaded into the second collar 522 to hold the collar522 holding the outer race.

A circular fence 526 surrounds the rotating platen 52 and capturesslurry and associated liquid centrifugally expelled from the platen 52.This slurry falls down to a trough 528 formed in the table top 23 andfurther into the drain channel 515 and drains through a hole 530 throughthe table top 23 to a drain pipe 532 connected thereto by screws 534passing through a flange 536 of the drain pipe 532 and threaded into thebottom of the table top 23. The narrow, winding passageway between theplaten 52 and table top 23 combined with the centrifugal force from therotating platen assembly 500 keeps the slurry away from the bearings518.

A platen motor assembly 540 is bolted to the bottom of the table top 23through a mounting bracket 542. The motor assembly 540 includes a motor543 with a output shaft 545 extending vertically upwards which is splinefit to a solid motor sheave 544. A drive belt 546 is wound around themotor sheave 544 and a hub sheave 548 joined to the platen base 512through a reservoir hub 550 and a platen hub 552. An example of theplaten motor is a Yasakawa SGMS-50A6AB with a gear box, which can drivethe platen 52 at a rotation rate in the range of 0 to 200 RPM.

SLURRY DELIVERY

At least two types of slurry feed may be used, a top dispensing tube anda bottom center feed. The bottom center feed will be described first.

An angular passage 554 is formed in the platen top 510 to supply slurryto the center of the platen 52. The angular passage 554 is aligned andsealed with an O-ring in a recess 556 connecting to a vertical passage558 in the platen base 512. The characteristics of the slurry feed tothe pad 54 from the center of the platen 52 are such that the rotationof the platen 52 tends to generally equally distribute the slurry overthe surface of the unillustrated polishing pad 54.

Such slurry supplies through the platen are known, but in the past theyhave used a rotary coupling on the platen hub or drive shaft. However,the use of abrasive slurry in a rotary coupling causes it to wear outrapidly or requires excessively frequent maintenance.

Rotating Slurry Reservoir

These problems are avoided by a reservoir system 5100 illustrated inmore detail in the enlarged cross section of FIG. 20. The outerperiphery of the reservoir hub 550 is formed with an upwardly extendingdam wall 5110 and an inward lip 5112. The dam wall 5110 and the platenhub 552 sealed to the central portion of the reservoir hub 550 forms arotating reservoir 5114 for slurry 5116. A stationary slurry feedassembly 5120, illustrated on the right, includes a bracket 5122attached to the bottom of the table top 23. The bracket includes atapped hole 5124 to which can be threaded a male end of a fitting forstationary slurry feed line. A horizontal passage 5126 bored and sealedin the bracket 5122 is connected to a vertical passage 5128 extendingdownwardly to the bottom of the bracket 5122 over the reservoir 5114 tosupply slurry thereto. A fluid level sensor 5130 extends downwardly fromthe bracket 5122 to detect the level of slurry 5116 in the reservoir5114 so that, when the level becomes too low, additional slurry issupplied from an externally controlled supply through the tapped hole5124.

A diaphragm pump 5140, illustrated in more detail in the yet furtherenlarged cross section of FIG. 21, pumps the slurry 5116 from thereservoir 5114 to the central hole 554 (FIG. 19) at the top of theplaten 52. The diaphragm pump 5140 principally consists of a lowerdiaphragm cavity 5144 formed in the reservoir hub 550, an opposed upperdiaphragm cavity 5146 formed in an overlying upper pump member 5148. Aflexible diaphragm 5150 is sealed between the two diaphragm cavities5146 and 5146, and the upper pump member 5148 is secured to thereservoir hub 550 by unillustrated threaded fasteners to clamp thediaphragm 5150.

The diaphragm pump 5140, which rotates with the platen 52, is poweredpneumatically by a fluid selectively supplied under varying pressures bya stationary pneumatic source installed in or adjacent to the machinebase 22. A positive pressure applied to the lower diaphragm cavity 5144causes the diaphragm 5150 to flex upwardly, while a negative pressurecauses it to flex downwardly. The flexing, together with a set of inletand outlet check valves to be described below, pumps the slurry fluid inthe upper diaphragm cavity 5146. The pneumatic fluid is supplied to thelower diaphragm cavity 5144 through a passageway 5152 connecting thelower diaphragm cavity 5144 to the lower side of the reservoir hub 550opposed to an O-ring sealing chamber 5154. A second passageway 5155 inthe the solid motor sheave 544 connects the O-ring chamber 5154 to atapped hole 5156 at the bottom of the motor sheave 544 to which isconnected a flexible fluid line 5157. As illustrated in FIG. 19, thefluid line 5157 is connected through a coupling 5158 to an axial passage5160 in a rotating motor shaft 5162. A rotary coupling 5164 connects therotating axial passage 5160 to the stationary pneumatic source via anunillustrated pneumatic line.

As shown in FIG. 21, the upper pump member 5148 overlying the diaphragm5150 seals the diaphragm 5150 to the reservoir hub 550 to prevent fluidleakage between the upper and lower diaphragm cavities 5146 and 5144.Two flow check valve assemblies, only a front one of which isillustrated, are formed in the pump member 5148 to prevent back flow offluid oppositely to the pumping direction. Each flow check valveassembly includes a cylindrical chamber having a large cylindrical upperpart 5170, a tapered middle part 5172, and a small cylindrical lowerpart 5174. A valve ball 5176 is placed in the cylindrical chamber. Theball 5176 has a diameter smaller than that of the cylindrical upper part5170 but larger than that of the cylindrical lower part 5174 so that itcan effectively seal itself against the tapered middle part 5172. Therespective flow check valve assembly is sealed when the fluid pressurein the respective cylindrical upper part 5170 is greater than that inthe respective cylindrical lower part 5170, and the sealing is assistedby gravity since the valve ball 5176 naturally seats itself on thedownwardly tapering middle part 5172. The tops of the cylindricalchambers are sealed with a generally rectangular seal member 5178clamped in place by a pump cover 5180 screwed into the upper pump member5148.

The unillustrated backside flow check valve assembly is used to supplyslurry to the top diaphragm cavity 5148 of the diaphragm pump 5140 andis positioned in the flow path between the slurry reservoir 5114 and topdiaphragm cavity 5148. The top of the cylindrical upper part 5170 isconnected by an unillustrated passage to the upper diaphragm cavity5146. The cylindrical lower part 5174 is opened to an unillustrated sumpportion of the reservoir 5114 so that slurry is always present in theright circular lower part 5176 and can flow into the upper diaphragmcavity 5146 when the diaphragm 5150 is pneumatically flexed downwardlyto provide negative pressure in the upper diaphragm cavity 5146.However, if the diaphragm 5150 is pneumatically flexed upwardly toprovide positive pressure in the upper diaphragm cavity 5146, the valveball 5176 seats against the tapered portion 5172 and thereby closes thesupply check flow valve assembly against any backward flow of slurry.

The illustrated frontside flow check valve assembly is used to feedslurry from the upper diaphragm cavity 5146 of the diaphragm pump 5140to the central aperture 554 at the top of the platen 52. The lowercylindrical part 5174 of the feed flow valve check assembly communicatesdirectly with the upper diaphragm cavity 5146. A passage 5184 in theupper pump member 5148 connects the upper cylindrical part 5170 of thefeed flow check assembly to a hook-shaped passage 5186 in the reservoirhub 550 and platen hub 552, which ultimately connects to the centralaperture 554 at the top of the platen 52. (It is noted that in interestof clarity some of the passages are illustrated differently thanactually embodied in our prototype, but the differences do notsignificantly affect the invention.) When positive pneumatic pressure,whether liquid or air, upwardly flexes the diaphragm 5150, the slurry inthe upper diaphragm cavity 5146 is pumped through the passages 5184 and5186 to the top of the platen 52. When the positive pneumatic pressureis released, the seating of the valve ball 5176 in the feed check flowvalve assembly prevents the back flow of slurry, particularly due to thehead created by the back pressure of slurry pumped above the level ofslurry 5116 in the reservoir 5114.

This configuration of the slurry feed eliminates the problem of having aslurry running through a rotary coupling and provides a high degree ofreliability as well as shortens the length of the slurry line whichmight get plugged if slurry were to sit in the slurry line for a longtime.

Overhead Slurry Dispenser

It is advantageous to additionally include an overhead slurry dispenser5200, as illustrated in schematic cross-sectional view in FIG. 22 and inplan view in FIG. 23. It includes a dispensing tube 5202 rotatablysupported on a dispenser base 5204 located on the table top 23 withinthe surrounding fence 25. The dispensing tube 5202 is rotatable over theplaten 52 and attached polishing pad 54 such that its dispensing end5206 can be located to one or more points adjacent to the wafer head110. As has been described before, the wafer head 110 is supported onthe carousel 90 and, during polishing, slides linearly across a diameterof the pad 54. FIGS. 22 and 23 are somewhat schematic in not showing thecomplete overhang of the carousel 90 over the pad 54. If the wafer head110 is performing over-center polishing, the end 5206 cannot be parkednear the center of the polishing pad 54. Either it is parked to the sideof the furthest outward position of the wafer head 110 or its motion issynchronized with that of the wafer head 110 to avoid any collision. Thedispensing tube 5202 is also rotatable to an off-platen position 5208 atwhich the dispensing end 5206 is positioned off the polishing pad 54 anddirectly over the table top 23. This dispensing tube 5202 is moved tothe off-platen position 5208 when it is desired to flush it so that theflushed liquid and possible debris are collected on the table top 23 anddrained from it without contaminating the polishing pad 54.

Preferably, the overhead slurry dispenser 5200 has two dispensing portsfor alternately or even simultaneously dispensing two slurries or aslurry and another liquid. As shown in the enlarged elevational view ofFIG. 24, the dispensing tube 5202 includes two supply tubes 5210 and5212 joined to each other and including respective downwardly projectingtube dispensing ends 5214 and 5216. One tube dispensing end 5214 shouldbe longer than and laterally separated from the other so as to minimizethe splashing of slurry from an active tube dispensing end to aninactive one, which would tend to cause slurry to dry and cake on theinactive tube dispensing end. Similarly, the middle portion of thedispensing tube 5202 extending horizontally over the pad 54 should be ata sufficient height above the pad 54 to reduce the amount of slurry thatsplashes from the pad 54 onto the dispensing tube 5202. The supply tube5210 and 5212 and other exposed parts of the slurry dispenser 5200should be composed of a material such as Teflon which is resistant tocorrosive slurry and is preferably hydrophobic.

The limited rotation of the dispensing tube 5202 allows the rotationalfluid coupling to be accomplished with two flexible supply conduits 5218and 5220 joined to respective supply tubes 5210 and 5212 or associatedfluid channels terminating at the bottom of the table top 23.

Slurry Supply

It is noted that the above slurry dispenser 5200 as well as slurryreservoir system 5100 and associated platen supply passage 554 of FIGS.19, 20, and 21 allow different slurries to be supplied to the threepolishing systems 50a, 50b, and 50c. Also, the drain 532 of FIG. 19below the platen 52 collects most of the excess slurry for thatpolishing station and can be isolated from corresponding drains at theother polishing stations. Hence, different slurries can be used at thedifferent polishing stations but their drains can be substantiallyisolated. The isolation alleviates disposal problems and permitsrecycling of slurry even in a complex process.

The polishing system 10 of the invention is intended for a variety ofpolishing processes that can be selected by the user and even changedwith a minimum of mechanical reconfiguration. Hence, the slurry deliverysystem should be both general and flexible and provide for cleaningfunctions for the lines which tend to clog with dried slurry. An exampleof such a slurry delivery module 5230 is schematically illustrated inFIG. 25. The figure illustrates a supply unit 5232 for all threepolishing stations 50a, 50b, and 50c and one of three flow control units5234 for respective ones of them. The plumbing connections adjacent tothe platen 52 are not illustrated and may be easily replumbed betweenthe slurry feed assembly 5120 illustrated in FIG. 20 for the slurryreservoir system 5100 and the two flexible conduits 5218 and 5220 of theoverhead slurry dispenser 5200 of FIG. 22.

The supply unit 5232 includes a bulkhead unit 5236 containing manypneumatic on-off valves and connecting piping. It also includes threesupply sources 5238a, 5238b, and 5238c, each of which includes a supplytank 5240, a supply tube 5242 and associated pump 5244, and a returntube 5246 to provide a recirculating source of slurry or liquid.Associated level monitors and fresh supply tubes are not illustrated butare well known in the art. It is anticipated that two supply source5238a and 5238b will be typically used for two different slurries whilethe third supply source 5238c will be used for a non-slurry liquidchemical, such as ammonium hydroxide. Of course, a greater or lessernumber of supply sources 5238 may be used depending on the polishingrequirements and the necessity to economize.

The bulkhead unit 5236 contain an on-off valve 5248 for each supply line5242 and a flow check valve 5250 for each return line 5246. Although theillustrated bulkhead unit 5236 uses only one supply valve 5248 for allthree polishing stations so that the same liquids flow to all threestations, additional valving would allow independent and separatesupplies. The bulkhead unit 5236 also receives nitrogen and deionizedwater (DIW) through on-off valves 5252 and 5254, both of which connectto a purge line 5256 which is gated to any of the supply sources 5238a,5238b, or 5238c through respective on-off valves 5258. The nitrogen orDIW is used to purge and clear various lines as required. The purgeconnections are not illustrated. For clearing clogged lines, the purgeconnections can be manually made since the supply sources 5238a, 5238b,and 5238c are located in an accessible area.

FIG. 25 shows only two supply units 5238a and 5238c connected to theflow control unit 5230 of the one illustrated polishing station 50a,50b, or 50c although the remaining supply unit 5238b could be connectedto one of the other polishing stations. Each flow control unit 5230includes two metering units 5260a and 5260b, each of which contains adiverter valve 5262a or 5262b connected to different recirculating pathsfrom the supply units 5238a and 5238c. A diverter valve selectivelyconnects a third port to a flow path between its first two ports, whichare in the recirculating path. The valved output of the diverter valve5262a or 5262b is routed through a bulk flow controller 5264 which willdeliver a liquid flow rate to the associated slurry port at the platen52 that is proportional to an analog control signal SET input to thebulk flow controller. It is anticipated that flow rates in the range of50 to 500 ml/min will be typically required, but the range may shiftdown to 13 ml/min and up to 2000 ml/min depending on polishing processthat is implemented. Preferably, the delivered flow rate is measured andreturned on a monitoring line MON. Although fluid equivalents to massflow controllers could be used for the bulk flow controller 5264, therequired high levels of reliability with corrosive pump fluids haveinitially required use of a metering pump, such as a peristaltic pumpwhich does not directly provide the monitoring function.

A line carrying deionized water is led through both metering units 5260aand 5260b, and respective diverter valves 5266 direct DIW through therespective bulk flow controllers 5264. The DIW is used to flush thelines and clean the polishing pad, but it may also be used in thepolishing process, for example, a polishing station dedicated tobuffing. Alternatively, a dedicated DIW line 5268 and associated on-offvalve 5270 may be connected to one of the slurry ports at the platen 52.

Pad Peeling

The polishing pad 54 on the surface of the platen 52 wears out over timeand has to be periodically replaced. One of the difficulties inreplacing a worn polishing pad is that strong pressure-sensitiveadhesive is used to attach the pad to the platen and the two remainstrongly bonded together over periods of use. In the past, to remove thepolishing pad it was necessary to use a large force to pull thepolishing pad away from the top of the platen to overcome the adhesiveseal between the pad and platen. This large force requires significantoperator involvement and time.

An embodiment of the invention for automatically peeling the pad 54 fromthe platen 52 is illustrated in the cross section of FIG. 19. Itincludes the option of injecting high pressure air or fluid through ablow port 560 opening at the top of the platen top 510 near its centerbut offset therefrom because the slurry port 554 is at the center. Thepressure tends to create a bubble between the pad 54 and platen 52 whichgradually expands and thus gently peels the pad 54.

The blow port is connected to four vertical passages 561, 562, 564, and565 formed in the platen 510, the platen base 512, the platen hub 552,and the reservoir hub 550 and is also connected thereafter to an angledpassage 566 in the solid motor sheave 544. These passages are joined toeach other by O-rings placed in recesses 568, 570, 571, and 572. Theangled passage 566 connects to a tapped hole 574, into which can bethreaded the fixed end of a quick-release fitting 576 of a high-pressureair line 578. During the polishing operation, the fixed end of thequick-release fitting is fixed on the platen assembly 500 and isrotating with the platen 52. When the platen 52 is stopped, thedetachable end of the quick-release fitting connected to thehigh-pressure hose 578 is freely connectable to the fixed end of thequick-release fitting to connect passages to the blow port 560.

In use, when it has been determined that the polishing pad 54 needs tobe replaced because is surface has been degraded, the platen 52 isstopped, and the operator or an automatic mechanism connects the twoparts of the quick-release fitting to thereby connect the high-pressureair supply hose 578 to the blow port 560. The air pressure so appliedwhile the platen is stationary injects air beneath the polishing pad 54in the area of the blow port 560 at the top of the platen 52 and tendsto create a bubble there, which gradually increases and has the effectof peeling the pad 54 from the platen 52. The bubbling effects reduces,if not eliminates, the force necessary to peel the polishing pad 54 fromthe platen 52. The opening 554 for the slurry located in the center ofthe platen 52 will be generally so small that the air released throughit will be negligible or it can be temporarily plugged by the userplacing his finger over the opening or otherwise providing some sort oftemporary seal. Of course, the quick-release fitting is disconnectedafter the pad has been removed and before the platen again is rotated.The removal and replacement of the polishing pad is thereforeaccomplished more easily than has been done in previously knownconfigurations.

Although it would be possible to completely automate the peeling processthrough a rotary coupling connecting the high-pressure air line 578 tothe blow port 560, the relatively infrequent need to change pads reducesthe desirability of the added complexity. High-pressure liquid ratherthan gas could alternatively be used for the peeling operation.

Intermediate Washing Stations

In the preferred operation of the invention, the wafers are sequentiallypolished at two or all three of the polishing stations 50a, 50b, and 50cshown in the top view of FIG. 18. One polishing method is a multi-steppolishing process in which, for example, a rough polish is followed bytwo successively finer polishes. One method of achieving increasinglyfine polishing is to use at the different polishing stations 50 slurrieshaving different characteristics or particle sizes. In this situation,it is important to avoid cross contamination of slurry between differentplatens; that is, to assure that the slurry, both particles andpolishing liquid, of one polishing station is completely removed from awafer before it is moved to the next polishing station. When wafers aretransferred between polishing stations 50, much of the slurry used inthe prior polishing step that is initially attached to the wafer as itis lifted from the pad drips from the wafer to the pad 54 and associatedplaten 52, as shown in FIG. 19, from whence much of it drips into thedrainage basin defined by the fences 526 surrounding the platens 52.However, some slurry remains attached to the wafer unless specialprecautions are taken, and this adhered slurry can contaminate the nextpolishing station, especially the subsequent polishing pad 54, in adegree that increases with time.

Therefore, in some highly sensitive processes, it is desirable toinclude the intermediate washing 80a and 80b, as shown generally in FIG.18, that are located between the platens 52 of neighboring polishingstations 50a, 50b and 50b, 50c. These intermediate polishing stationswash wafers passing between the neighboring polishing stations anddispose of the cleaned slurry so as not to contaminate the nextpolishing station. It is also desirable to additionally include anotherintermediate washing station 80c between the last polishing station 50cand the transfer station 70. As will become evident in some laterdiscussions, the intermediate washing stations 80 can be used for alight buffing of the wafers and well as removing slurry and loosematerial. Furthermore, a preliminary intermediate washing station 80aacan be included between the transfer station 70 and the first polishingstation 50a. This replication of intermediate washing stations haslittle impact on wafer throughput because they can all simultaneously bewashing or buffing respective wafers.

The intermediate washing stations 80 could be retractable or evenhorizontally movable. However, in a configuration according to theinvention, they are stationary with an upper surface slightly above thelevel of the polishing surface of the polishing pad 54 so that, when thewafer head 100 raises the wafer from the platen 52, moves it over thewashing station 80, and lowers it onto the washing station 80, the wafer40 comes into contact with the washing station 80 at a position abovethat of the neighboring platen 52. The gap is essential because thewafer on the washing station 80 will also overlie the two neighboringplatens 52. The intermediate washing station 80, in general, provides asealed opening below the surface of the wafer head 110. It usuallyincludes a wash chamber which can be sealed by placing the wash waferhead on a lip of the chamber.

In a configuration according to an embodiment of an intermediate washingstation 800 of the invention shown in the three perpendicularly arrangedcross-sectional views of FIGS. 26A and 26F and plan view of FIG. 26G, awash chamber 810 has an elongate upper opening 812 having the shape of arelatively narrow elongated slot located between adjacent platens 52. Asshown in FIG. 26G, two sides 814 of the opening 812 have lengthssufficient to generally reach across the wafer 40 when the center of theopening 812 is aligned with the center of the wafer 40, and the othertwo sides 816 have arcuate shapes corresponding to the circumference ofthe wafer 40.

The intermediate wash station 80 is formed by a spray pipe 820 extendingalong the elongate opening 812 and having a number of verticallyoriented nozzle openings 822. The ends of the spray pipe 820 are sealedby plugs 824, and the spray pipe 820 is fixed to a support member 826having an upper end generally defining the opening 812 of the washchamber 810. A tapered elastic seal 828 is placed inside the supportmember 826 to define the lateral sides of the washing chamber 810. Theseal 828 has an upper end conforming to the shape of the opening 812 ofthe wash chamber 810 and protruding slightly above the top of thesupport member 828. Its lower end is supported on the spray pipe 820 soas to leave exposed the nozzle openings 822 and the drain opening to beshortly described. Preferably, the elastic seal 828 is formed of a foamyor fibrous material that acts as a barrier to break a spray but thatallows the flow of water and entrained slurry through it. Thereby,slurry does not become embedded in the seal 828, and accreted slurrycannot scratch the wafer 40. Exemplary seal materials include thematerial used for polishing pads.

As best shown in FIG. 26F, a supply pipe 830 is sealed to the bottom ofthe spray pipe 820 at a supply opening 832 in a lower side andlongitudinal end of the spray pipe 820. A drain pipe 834 is sealed tothe supply pipe 820 and passes from the bottom side to the top sidethereof at a drain opening 836. When washing is desired, a washingliquid 840, such as deionized water, is supplied under pressure throughthe supply pipe 830 into the interior of the spray pipe 820. Whensufficient washing liquid 840 has been supplied to fill the spray pipe820, any further washing liquid is sprayed through the nozzles openings822 in sprays to cover the portion of the wafer 40 overlying theelongate opening 812. Excess washing liquid and entrained slurry rinsedfrom the wafer 40 fall down to the bottom of the washing chamber 810 anddrain out through the drain opening 836 for recycling or disposal.

The operation of the intermediate washing station will now be described.When a polishing step at a first polishing station, e.g., 50aillustrated in FIG. 26A, has been completed, the rotation of the waferhead 110 is stopped, the lower end of the wafer head 110 holding thewafer 40 is raised from the platen 52 and polishing pad 54 by a shortdistance of, for example, 1/4 inch (6 mm), the slide 908 holding thewafer head 110 is placed at a radial position of the carousel 90 alignedwith the intermediate washing station, e.g. 80a, and the carousel 90 isrotated to move the wafer head to a position at which, as shown in FIG.26B, places the center of the wafer head 110 and its wafer 40 over thecenter of the intermediate washing station 80a. The lower end of thewafer head 110 is then lowered, as shown in FIG. 26C, to place the waferinto low-pressure contact with the elastic sealing member 828 of theintermediate washing station 80a so as to provide a water barriertherebetween but not to damage the wafer 40. The required pressure iscomparable to or less than those used at the polishing stations 50. InFIGS. 26D and 26F, the washing liquid 840 is pressurized in sufficientamount to wash the portion of the wafer 40 exposed above the washingchamber 810, and the washed off slurry drains out through the drain pipe838.

Preferably, the wafer 40 is washed continuously, as illustrated in FIGS.26D and 26F, as the wafer head motor 1012 continuously rotates the wafer40 past the elastic sealing member 828. Of course, the material of thesealing member 828, the applied force, and the rotation speed must bechosen such that the wafer 40 is not gouged or scratched as it slidesover the water-tight seal with the sealing member 828. A large number ofrevolutions during the washing will produce a buffing effect.

Alternatively, the wafer could be washed in discrete steps as it islowered, washed, raised, and partially rotated to a new position so asto wash all portions of the wafer.

A combination of these methods can be used as long as wash water is notpermitted a path to escape from the wash chamber 816 and directly spraythe bottom of the multi-head carousel 90 since such spraying could causethe splash shield to be breached. The wafer head can be slowly spun sothat at least all of the surfaces are cleaned or are essentiallysqueegeed off by the seal between the washing station and bottom of thewafer head and the squeegeed liquid is drained away from the bottom ofthe chamber. The wafer head can then be raised and moved to itspolishing location at the next platen. This ensures that at least allloose particles from one wafer head are removed.

Although the above description involves only a single wafer at aparticular intermediate washing station 80, the carousel positions allthe wafer heads 110 over respective washing stations such that washingstations are present at all those angular positions. Therefore, two,three, or even four wafers can be simultaneously washed according to theabove process by multiple washing stations 80.

After completion of the washing of the complete wafer 40, the wafer head110 raises the wafer 40 off the sealing member of the elastic sealingmember 828 and, as shown in FIG. 26E, the carousel 90 rotates the waferhead 110 and attached wafer 40 to the next polishing station 50b.

A design for an alternative intermediate wash station 80' is illustratedin cross section in FIG. 27 and in plan view in FIG. 28. A wash housing850 having an enclosed wash cavity 852 is fixed to the top of the tabletop 23. A linear wash aperture 854 is formed at the top of the washhousing 850 to a length substantially equal to the diameter of the wafer40 and is generally aligned along the boundary between two polishingstations 50 and perpendicularly to the rotation direction of thecarousel 90. However, it is noted that the intermediate washing stations50 or 50' can advantageously be placed at corresponding positions beforeand after the polishing sequence for a total of four such intermediatewashing stations in the three-pad system of FIG. 6A.

A contact pad 856 is glued with adhesive to the top of the wash housing850 except above the wash aperture 854 to thereby allow the wafer head110 to gently press a wafer 40 against the top of the washing station80' without scratching the wafer 40 but still forming a fairlywater-tight seal. Such a contact material needs to be soft and pliableand can be similar to the elastomeric sheet placed on the pedestal 72 ofthe transfer/wash station 70 or can be a fibrous or foamy pad similar toa fine polishing pad material. Alternatively, the contact material maybe incorporated into a removable top which is easily connectable to thewashing housing 850.

A ridge nozzle mount 860 is fixed to the table top 23 and rises withinthe wash cavity 852 of the wash housing 850. A ridge peak 862 at its topis positioned just below the wash aperture 854 and includes severalvertically directed nozzle holes 864 having diameters, for example, of0.025" (0.64 mm). The nozzle holes 864 are connected to a longitudinallyextending supply passage 866 connected to a centrally located verticalsupply passage 868, which is sealed by an O-ring recess 870 to avertical passage 872 in the table top 23 having a tapped hole 876 at itsbottom to which can be coupled a selectively applied supply of washliquid. A number of horizontally extending scuppers 878 extend throughthe bottom of the wash housing 850 at its juncture with the table top 23so that wash liquid falling to the bottom of the wash cavity 852 canflow outwardly to the top of the table top 23, which includes severaldrains for excess slurry and other polishing liquids.

The top of the contact pad 856 above the wash housing 850 is slightlyabove the top of the platen 52 of the polishing stations 50. After awafer 40 has been polished at one polishing station 50, the wafer head110 lifts the wafer 40 from the platen and brings it above theintermediate washing station 80' and lowers it thereagainst. The nozzles864 eject wash liquid towards the wafer 40, the debris laden liquidfalls within the cavity 852 to be drained through the scuppers 878.

The wafer 40 can be polished either by the stepwise washing describedpreviously or by slowly and continuously rotating the wafer head 110 andattached wafer 40 in loose contact with the contact pad 856. If theporosity of the elastomeric seal 856 is properly chosen, the wafer 40 issqueegeed as it passes over the intermediate washing station 80'.

In the prior art, a separate polishing station was required to buff thewafer 40 at the end of polishing, that is, to very lightly polish thewafer so as to remove any dust and debris. The buffing was done on abuffing pad similar to a polishing pad. The operation of theintermediate polishing station, especially one at the end of thepolishing sequence, performs very similar functions to those of buffing.As a result, the inclusion of intermediate polishing stations frees thethird polishing station for actual polishing, thus substantiallyincreasing the throughput of the system.

Furthermore, one or more of the intermediate washing stations 80 or 80'can be considered to be a separate polishing station. Therefore, one ormore washing stations 80 or 80' can be angularly arranged relative tothe polishing stations 50 so that the wafer heads 100 simultaneouslyoverhang both the washing station 80 or 80' and the polishing stations50. As a result, the washing or buffing at the washing station can beperformed simultaneously with the polishing at the polishing stations,thereby increasing the throughput of the polishing apparatus.

Pad Conditioner

The polishing pad, prior to its needing to be completely replaced, needsto be occasionally (or regularly) conditioned to prevent its surfacefrom becoming glazed. In the embodiment described herein, the padconditioner is a rotating disk having a rough surface that iscontinuously brought into contact with the rotating polishing pad duringconditioning and is swept back and forth across the pad 54 from itsperimeter to the center. Other types of conditioners are possible. Theconditioning member can be planar but non-circular, it can be acylindrical member having a circumferential surface contactable with thepad, or it may be one or more styli, among other possibilities. Thesurface of a conditioner can be abrasive, be toothed, or have sharpaperture edges, among other possibilities. The surface of theconditioning member can move relative to the pad, the conditioner membercan roll over the pad and primarily emboss its surface pattern in thepad, the conditioning member can be dragged as a stationary body acrossthe pad, or it can be rotated in different planes relative to the pad,among other possibilities. All such conditioning members are includedwithin the concept of a conditioning head positionable over and movablerelative to the polishing pad.

In overview, as shown in the cross section of FIG. 29, the padconditioner 60 includes a conditioner head 64 suspended on the distalend of an arm 62. The proximal end of the arm 62 is supported by asupport assembly 65 which can rotate the entire arm 62 in the plane ofthe wafer so as to place the conditioning head 64 in place for padconditioning and to sweep it over the pad 54, can slightly elevate theconditioner head 64 by about 11/4" (32 mm) to put the conditioner head64 in selective contact with the pad 54, and rotates the conditioninghead 64 through a belt drive.

Conditioner Head

The conditioner head 64 holds within a recess 610 on its bottom face atoothed or otherwise very abrasive surface conditioning disk 612 orother generally cylindrical member. Its downwardly facing surface 614 isrough enough that, when engaged with a glazed polishing pad 54 andmoving relative thereto, it can deglaze the pad 54 by scouring itssurface.

The conditioner head 64 is illustrated in more detail in the crosssection of FIG. 31. The conditioning disk 612 includes a central, loweraperture 616 at the center and bottom of which is located at theeffective rotational center 618 of rotation of the conditioning disk612. The effective rotational center 618 is the point around which, whenthe compression and varying lateral consistency of the pad 54 andconditioner surface 614 are taken into account, provides a point aboutwhich the torque can be minimized because the rotational frictionalengagement between the conditioning surface and the polishing padproduces no net torque relative to that point in the vertical direction.

As additionally illustrated in the perspective view of FIG. 30, theconditioning disk 612 is held in the recess 610 at the bottom of aconditioner head face plate 620 by a flexible holding pad 621 placedinto the recess 610 and having a sticky face that adheres to the faceplate 620 and a lower magnetic face. The conditioning disk 612 is fitinto the recess 610 adjacent to the holding pad 621. The conditioningdisk 612 is made of a magnetic material that is held to the magneticside of the holding pad 621, and its other side is impregnated withdiamonds for scraping the polishing pad 54 against the edges of atriangular array of circular holes 615 penetrating the conditioning disk612. The holes have diameters of about 1/8" (3 mm). Such a conditioningdisk 612 is available from TBW Industries of Furlong, Pa. as agrid-abrade model. A gate 619a is formed in a wall 619 of the recess 610to allow the conditioning disk 612 to be pried from the recess 610.

It is understood that the perforated conditioning disk 612 of FIG. 30 isillustrative only and other conditioning members are included within theinvention.

Gimbal Drive

As illustrated in FIG. 31, a novel gimballing structure connects theconditioner head face plate 620 and attached conditioning disk 614 tothe conditioner arm 64. Any gimballing structure allows rotationalmovement to be imparted to a disk-like structure while the drive axis istilted relative at angle which is not necessarily perpendicular to thedisk. However, as illustrated in FIG. 32, a conventional gimballingstructure 621 has a gimbal rotational center 622 (it is assumed that thetwo horizontal axes of rotation in the gimbal structure intersect) aboutwhich a drive axis 624 and a normal axis 626 can deviate by an angleα_(gimbal). The conventional gimbal rotational center 622 is locatedabove the horizontal torque center 627 at the interface between theconditioning disk 612 and the polishing pad 54. The offset from thehorizontal torque center 627 means that a finite vertical torque 628 iscreated as the conditioning disk 614 is swept over the pad 54 andexperiences net horizontal linear frictional force offset from thegimbal center rotational center 622. The net vertical torque 628 may bedemonstrated in that the shaft rotating the conditioning disk 612 andlinearly translating it along the surface exerts a resultant force R inthe horizontal plane that passes through the gimbal rotational center622 while the net linear frictional force F that the pad 54 exertsagainst the translating conditioning disk 612 lies at the interfacebetween the conditioning disk 612 and the pad 54. That is, even thoughthe two forces are equal though opposite, the two forces are separatedby a moment arm which creates the finite vertical torque 628. Thevertical torque 628 causes a leading edge 630 of the conditioning disk612 to have a greater vertical pressure against the conditioning pad 54to be deglazed than the vertical pressure applied against a trailingedge 632 of the conditioning disk 612.

The vertical torque 628 causes the polishing process to abrade theleading edge 630 more than the trailing edge 632. This torque whichcauses differential loading and polishing is increased when theconditioner head is swept in the direction having the larger downwardpressure so that the sweep force is partially converted to a downwardforce on the leading edge.

This problem of differential polishing is reduced or nearly eliminatedin the geometry of the head according of FIG. 33 in which the horizontaltorque center 627 is coincident with the gimbal rotational center 622 ata common center 636. Both the resultant force R' from dragging theconditioning disk 612 across the pad 54 and the frictional force betweenthe conditioning disk 612 and the pad 54 lie within the same plane atthe interface between the conditioning disk 612 and the pad 54. Therotational torque 628 resultant from sweeping over a frictional surfaceis reduced to zero because the torque center 628 lies within the planeresisting that torque, that is, the resultant force R' and frictionalforce F' lie within the same plane with no moment arm between them. As aresult the differential loading caused by an offset gimballing center622 is significantly reduced.

Referring to the perspective view of FIG. 34, the oscillation of theconditioner arm 62, that is, its sweep across the polishing pad 54 fromits center to its perimeter, is performed by rotation of the conditionersupport shaft housing 1630 being rotated by a harmonic drive 1668coupled to an arm sweep drive motor 1670. This structure will bedescribed more fully later, The conditioner arm 62 is turned by theconditioner sweep drive motor 1670 through the set of stub shafts 1642bolted to the drive housing 1630 discussed above.

Referring back to the schematic of FIG. 33 of the novel gimballingstructure, as the conditioner disk 612 is forced along the surface ofthe glazed pad 54, a frictional force F' is developed. However, becauseof the centrally placed common center 636, the motive force R' is equal,opposite, parallel, and in line. As a result, there is no net torque onthe conditioner head.

This effect can be achieved by a ball-and-socket joint 640 in which thespherical center of symmetry lies on the interface between theconditioning disk 612 and the polishing pad 54. Additional means preventthe socket part 642 from rotating within the horizontal plane withrespect to the ball part 644. By placing the center of theball-and-socket connection through which force is transmitted at thesurface of the polishing pad 54 in direct opposition to the frictionalforce, this configuration eliminates any tendency of the head to rotateand create a greater pressure on one side of the conditioning head thanon the others, as happens in the prior art.

A particular design according to the invention, as shown in thecross-sectional view of FIG. 31, attaches the backside of theconditioning disk 612 including the abrasive conditioning head surface614 to a cylindrical lower ball joint part, having attached thereto inits lower, inner corner a bearing element 652 having a convex annularsegmented surface 654 having a center of curvature at the common center618. This part creates a ball of a ball-and-socket joint.

In opposition to the just described ball part, a socket part includes aconditioner head shaft 656 having a concave annular segmented surface658 in opposition to the convex surface 654 and having a center ofcurvature at the common center 618. A ball-bearing cage 660 capturesseveral bearing balls 662 rolling between the convex surface 654 of thebearing element 652 and the concave surface 658 of the conditioner headshaft 656. The bearing balls 662 allow the conditioner head shaft 656 tonutate (within the two vertical planes) with respect to the conditionerhead face plate 620 and thus the pad 54. However, a very soft O-ring 664(preferentially durometer 40) is captured in an annular, inwardly facingrecess 666 of the bearing element 654 and faces an outwardly facing wall668 of the conditioner head shaft 656. The compressibility of the O-ring664 within the confining recess 666 limits the nutation of theconditioner head shaft 656 with respect to the bearing element 654 to afew degrees, more than enough for the operation of the conditioner head64. The non-infinite compressibility, in fact, violates the assumptionof no vertical torque in the gimballing structure. The nutation allowsthe conditioning disk 612 to move within a small range of polar anglesto allow for any slight variations in the surface of the polishing pad54 without providing greater pressure on one side of the conditionerhead facing plate 620 than on the other.

A necked nut 670 is threaded onto an upper rim 672 of the conditionerhead bearing element 620, and its upper neck 672 captures but onlyloosely surrounds an outer flange 674 of the conditioner head shaft 656,and its possible engagement presents an ultimate limit to the nutationof the conditioner head shaft 656 with respect to the bearing element656. A shoulder bolt 676 is threaded into the bottom center of theconditioner head shaft 656. Its downwardly facing head 678 is capturedon the upward side by an inwardly facing lip 680 of the bearing element650. The selective engagement of the head 678 of the shoulder bolt 676and the lip 680 of the bearing element 650 prevents the conditioner headbearing element 620 from falling from the conditioner head shaft 656when the conditioner head 64 is lifted from the polishing pad 54.

The ball bearings 662 would ordinarily allow the free azimuthal rotationof the bearing element 652 and attached conditioning disk 612 withrespect to the conditioner head shaft 656. However, a number ofperipheral drive pins 682 (only one of which is shown in FIG. 31) areloosely captured in paired drive pin holes 685 and 686 in theconditioner head bearing element 620 and the conditioner head driveshaft 656 to prevent any substantial azimuthal motion therebetween. Thatis, the drive pin holes 686 in the conditioner head shaft 656 do nottightly capture the drive pins 682 in a polar direction so as to allowthe limited nutation of the conditioner head shaft 656 with respect tothe conditioner head bearing element 620, but they capture the drivepins 682 laterally to prevent substantial relative azimuthal rotation.

The gimballing of the conditioner head allows planar rotational drivefor the conditioning disk of the conditioner head but allows theconditioner head to tilt somewhat from the normal to the polishing padbeing conditioned. The gimbal drive, because of its low center ofrotation, prevents differential conditioning of the substratetherebeneath.

The outer races of two annular bearings 688 are spaced by an outerannular spacer 690 and held by a top outer collar 692 screwed to abottom outer collar 694 with a biasing annular spring 696 between thelower annular bearing 688 and the bottom outer collar 694. The top outercollar 692 includes a lower, outer skirt 693, which presents alabyrinthine path for slurry and other contaminants from reaching thebearings 688 supporting the conditioner head shaft 656.

This assembly is suspended by screws 1602 countersunk into a generallyU-shaped arm body 1604 and tapped into a lower flange 1608 of the uppercollar 692.

In assembly, the lower part of the conditioner head is raised into thecenter of the annular bearings 688 with the inner race of the lowerannular bearing 688 resting on a ledge 1610 of the conditioner headshaft 656. An inner spacer 1612 separates the inner races of the twoannular bearings 688. The inner race of the upper annular bearing 688 iscaptured by a cornice 1614 of a toothed sheave 1616. A bolt 1618 pressesthe sheave 1616 as it is threaded into the conditioner head shaft 656and holds the inner races of the annular bearings 688.

Conditioner Arm and Support

Referring to the full cross section of FIG. 29, the enlarged crosssection of FIG. 35 and the partial perspective of FIG. 34, theconditioner arm 62 supports and raises the conditioner head 64, sweepsit across the pad 54 being conditioned, and encloses the belt assemblypowering the conditioner head 64.

The arm body 1604 includes a distal end wall 1618 and a channel cover1620 screwed into the arm body 1604 to form a housing 1622 enclosing thedrive belt assembly and protecting it from contamination by the slurry.The drive belt assembly includes a toothed drive belt 1624 wrappedaround the toothed head sheave 1616 attached to the conditioner head 64and also around a toothed drive sheave 1626 in the arm support 65. Atoothed drive belt 1624 is required because of the varying torquerequired of the drive belt 1624 as the conditioner head 64 conditionsdifferent surfaces.

As shown in FIGS. 34 and 35, the rotatable support housing 1630rotatably supports a proximal end 1632 of the arm body 1604 about ahorizontal nutation axis 1634. The vertically extending support housing1630 includes two flats 1636 in which are tapped four respectiveretaining holes 1638. When the flats 1636 of the support housing 1630are located within the channel 1622 of the arm body 1604, two shaftbases 1640 having respective stub shafts 1642 are attached onto theflats 1636 by screws held in holes 1644 countersunk in the flanges ofthe shaft bases, and the screws are threaded into the retaining holes1638 in the support housing 1630. The outwardly extending stub shafts1642 are rotatably supported by the inner races of spherical bearings1646 so as to be self-aligning and to accommodate misalignment betweenthe stub shafts 1642. The outer races of these bearings 1646 areattached to bearing cover plates 1648, which are fixed to verticalskirts 1650 of the arm body 1604 by screws passing through bore holes1652 in flanges of the bearing cover plates 1648 and threaded intotapped holes 1654 in the arm skirts 1650 to thereby establish thehorizontal nutation axis 1634.

Thereby, the proximal end 1632 of the conditioner arm body 1604 ispivotably supported about the horizontal nutation axis 1634, and theconditioner arm body 1604 is also rotatable in the horizontal plane bythe rotation of the support housing 1630.

The rotation of the conditioning arm 62 about the horizontal nutationaxis 1634 is effected by an hydraulic ram 1656 connected to a pin caughtin two horizontally holes 1658 of a yoke 1660 extending from the back ofthe arm body 1604 and also connected to a pivot support plate 1662 thatis attached to and rotates with the shaft housing 1630. Extension orretraction of the hydraulic rain 1656 either presses the conditioner arm62 and the attached conditioner head 64 toward the polishing pad 54 witha specified pressure as controlled by the pressure provided to thehydraulic ram 1656 or alternatively raises the conditioner arm 62 andhead 64 away from the polishing pad 54 for storage or maintenance.

As illustrated in FIGS. 34 and 35, the drive sheave 1626 for the belt1624 is fixed to an upper end of a drive shaft 1664 at a point above thehorizontal nutation axis 1634. The drive shaft 1664 passes verticallywithin the shaft housing 1630. At its upper end, it is connected to thepivot support plate 1662 and a skirt 1663 protecting the bearings. Itslower end holds a gear 1665 which is coupled to a gear 1667 on theoutput shaft of a conditioner head motor 1666 to provide the motivepower for the rotation of the conditioning disk 612. The conditionerhead motor 1666 is mounted on a motor bracket 1676 fixed to the tabletop 23.

As a result of the geometry, the actuator 1656 does not cause the drivesheave 1626 to pivot with the conditioner arm body 1604; however, thehead sheave 1616 does pivot with the conditioner arm body 1604.Therefore, because of the offset between drive sheave 1626 and thenutation axis 1634, the tension in the drive belt 1624 mounted betweenthe drive sheave 1626 and the head sheave 1616 is reduced as theconditioner arm 62 is raised and is increased as the conditioner arm 62is lowered. (The variations of tension with tilt angle would be oppositeif the drive sheave 1626 were located below the nutation axis 1634.) Thearrangement of the drive sheave 1626 offset above (albeit slightly) thecenter 1634 of vertical pivoting, also has an effect on the tension inthe drive belt 1624. As the arm 62 pivots downward toward the polishingpad 54, the tension in the belt 1624 increases, and, as the arm 62pivots away from the polishing pad 54, the tension in the belt 1624decreases. This increase and decrease in belt tension will combine withthe force from the hydraulic ram 1656 to affect the pressure of theconditioner head 64 on the polishing pad 54. The increase of tension ofthe belt 1624 will oppose the force generated by the hydraulic ram 1656tending to press the conditioning head 64 toward the polishing pad 54.An increase in tension will tend to lift the arm 62, while a decrease intension will tend to let the arm 62 press with greater force toward tothe underlying polishing pad 54.

In this arrangement, a constant coefficient of friction between theconditioner head 64 and the polishing pad 54 will provide a certainnominal tension in the drive belt 1624, which together with the forcefrom the hydraulic ram 1656 provides a certain nominal pressure betweenthe conditioner head 64 and the polishing pad 54 regardless of smallvariation in the height of the interface between the conditioner head 64and the polishing pad 54. If the friction between the conditioner head64 and the polishing pad 54 increases, as in those instances when arough polishing pad surface is encountered (which requires no additionalroughening/conditioning as the surface is already rough), the increasein the coefficient of friction will cause an increase in the forceneeded to continue to rotate the conditioning head 64 at a constantspeed. The increase of force will cause the tension in the conditionerdrive belt 1624 to increase, thus tending to raise the conditioner head64 off the polishing pad 54 to thereby reduce the pressure and thusabrasion of the conditioner head 64 on the polishing pad 54. Conversely,when the conditioner head 64 encounters an area having a low coefficientof friction, such as a glazed area on the surface of the polishing pad,resistance to rotation of the conditioner head 64 will diminish, therebydiminishing the tension in the conditioner head drive belt 1624. Thereduction of tension will reduce the force of the drive belt 1624,thereby tending to lower the conditioner arm 62 and thereby causing theconditioner head force on the polishing pad to increase, to bite moreinto the polishing pad, and to thus provide additional conditioning atthese location of glazing or low coefficient of friction.

The drive sweep motor 1670, shown in FIGS. 29 and 35 sweeps theconditioner arm 62 in an oscillatory path across the polishing pad 54between its center and its perimeter. The drive sweep motor 1670 ismounted to the motor bracket 1676 at the bottom of the table top 23. Agear 1672 on its output shaft is coupled to a rim drive gear 1674 of theharmonic drive 1668, which multiplies the transmitted torque. Anexemplary harmonic drive for the pad conditioner 60 is available fromHarmonic Drive Technologies, Teijin Seiki Boston, Inc. of Peabody, Mass.in unit size 25. The belt drive shaft 1664 passes along the central axesof the harmonic drive 1668 and the rim gear 1674. The high-speed,low-torque side of the harmonic drive 1668 is fixed to the motor bracket1676, and the low-speed, high-torque side is fixed to the shaft housing1630.

The conditioner arm 62 is horizontally turned through the set of stubshafts 1642, bolted between the arm body 1604 and the shaft housing1630, as discussed above. A conditioner head motor 1666 is connected tothe drive shaft 1664 through a set of gears in a gear housing 1672 fixedto the table top 23. The drive shaft rotates the drive belt 1624, theconditioner head 64, and hence the conditioning disk 612.

The pad conditioner 60 of FIGS. 29 through 35 can be used in a number ofdifferent modes, all controllable and selectable by the softwareincorporated into the controller computer for the polishing system.

The polishing pad 54 can be conditioned while polishing is interruptedat that pad. The wafer head 110 is withdrawn to its radially innermostposition, its bottommost portion is raised so as to separate any waferheld in the wafer head 110 above the pad surface, and the platen 52rotates as the conditioner arm 62 sweeps the rotating conditioner head64 in contact with and across the rotating pad 54 from its periphery toits center.

Alternatively, the polishing pad 54 can be conditioned while polishingcontinues at that pad, that is, in real time. The sweep of theconditioning head 64 generally extends across the outer portions of thepad 54 (as viewed from the center of the table top 23) while the waferhead 110 and its wafer 40 are swept across the inner portions.Nonetheless, the two sweeps may need to be synchronized to avoidcollision. Synchronization is obviously required for real-time padconditioning performed concurrently with over-center polishing since thewafer head 110 passes over and past the pad center 54a and this portionof the pad 54 requires conditioning.

Conditioner Head Cleaning Cup

The conditioning disk 614 of the conditioner head 64, as it sweepsacross the polishing pad 54, tends to become covered with slurry on itsabrasive face and outer surfaces adjacent to the polishing pad 54. Whilethe conditioner head 64 is operating on the wet surface of the polishingpad 54, slurry which is present on the surfaces of the conditioner head64, does not have time to dry and is easily replenished by new wetslurry particles as the conditioning process continues. However, duringtimes of inactivity, for example, when the conditioning head is storedduring polishing but most particularly when the entire apparatus is notoperating for a variety of reasons such as maintenance, the conditionerhead will tend to dry out and the slurry that is coated onto theconditioner head tends to form a rock-hard cake or cause the sodiumhydroxide in the slurry to crystallize on one of the surfaces of theconditioner head. It is then difficult to remove the caked-on slurry orcause the crystallized sodium hydroxide to return to a solution.

To obviate this problem, as shown in the general plan view of the tabletop 23 in FIG. 18, a cleaning cup assembly 68 is associated with eachpolishing station 50a, 50b, and 50c to store the inactive conditionerhead 64 in an aqueous environment.

As illustrated schematically in cross section in FIG. 36A, each cleaningcup assembly 68 includes a cleaning cup 2610 that is mounted to a shaftof a motor 2612 which can rotate the cleaning cup 2610 to an inactiveposition at which the conditioner arm 62 lowers the conditioner head 64into the cleaning cup 2610 when the conditioner head 64 is to be stored.A more complete illustration of the structure including the fluid linesis shown in FIG. 37. The inactive position is illustrated in the planview of FIG. 18 for the polishing station 50c.

As illustrated in FIG. 36B, when the conditioner head 64 is to bereturned to operation to condition the polishing pad 54, the conditionerarm 62 lifts the conditioner head 64 out of the cleaning cup 2610. Then,as illustrated in FIG. 36C, the motor 2612 rotates the cleaning cup 2610to inactive position, also illustrated in plan view in FIG. 18 forpolishing stations 50a and 50b. Returning to FIG. 36C, the conditionerarm 62 then lowers the conditioner head 64 onto the polishing pad 54mounted on the platen 52. When the conditioning operation is completed,the conditioner head 64 is raised and the washing cup 2610 is swung backto the position of FIG. 36B, at which position the conditioner head 64is lowered back into the cleaning cup 2610, as in FIG. 36A, for storageso that the slurry and sodium hydroxide attached to the conditioner head62 remain in solution or are diluted and removed.

The washing cup assembly 68 is illustrated in cross section in FIG. 37,and the washing cup 2610 is illustrated in plan view in FIG. 38. Thewashing cup 2610 includes a central basin 2614 defined by a nearlycircular weir 2616 of sufficient size and depth to receive the bottompart of the conditioning head 64. The weir 2616 is shaped to provide alongitudinal slip 2618 having at its outside end an aperture to avertically extending wash supply line 2620 having a diameter of 1/8"(3.2 mm). Water or another cleaning solution is circulated through thecup 2610 from the wash supply line 2620. It is possible that, as theconditioning head 64 is lowered into the basin 2614 of the washing cup2610, the conditioning head 64 would splash the wash solution containedtherein. Therefore, it is recommended that, prior to lowering of theconditioning head 64 into the washing cup 2610, the basin 2614 bedrained through the vertical supply passage 2620, which can beaccomplished by plumbing and three-way valves connected to the supplyline 2632.

A perimeter drain 2622 is formed between the outside of the weir 2616and a slightly higher, surrounding dam 2624. Both ends of the perimeterdrain 2622 extend outwardly parallel to the slip 2618 to two drain holes2625 joined to a common vertically extending drain passage 2626 having adiameter of 1/4" (6.4 mm). Whatever fluid overflows the basin 2614 iscaptured in the perimeter drain 2622 and is drained away through thedrain passage 2626.

The washing cup 2610 is mounted on its support side to a rotatable shaft2628, also formed with the vertical supply and drain passages 2620 and2626, and the passages 2620 and 2628 between the shaft 2628 and thewashing cup 2610 are sealed by unillustrated seals in recess. The shaft2628 is mounted through the table top 23 by a support bearing 2630.Since the rotation of the washing cup 2610 is relatively limited,flexible supply and drain lines 2632 and 2634 can be directly connectedto the respective passages 2620 and 2626 in the shaft 2628 throughconnections 2636 and 2638. The washing liquid drained through drain line2634 can either be disposed of or recycled through the supply line 2632.To prevent splashing, it is preferred that the central basin 2614 bedrained while the washing cup 2610 is being moved and when theconditioner head 64 is lowered into the washing cup 2610. The centralbasin 2614 can be drained through the wash supply line 2620 and theflexible supply line 2632 with a three-way valve being connected on theflexible supply line 2632 to change between the wash fluid source andthe drain. The motor 2612 is fixed to the bottom of the table top 23with a bracket 2640 and is geared to a side of the shaft 2628 throughunillustrated gearing.

Because of the greater height of the outside dam 2624, as shown in FIG.37, there is usually no loss of fluid from the cleaning cup assembly,and fresh cleaning solution is supplied or circulated as required tokeep the cleaning solution fresh so that the conditioner head 64 can bestored indefinitely without slurry or chemical crystal caking andcreating a problem on the surface of the conditioner head.

FIGS. 39A, 39B, and 39C show the relative motions of the conditioner arm62, the wafer head 64, and the polishing platen 52 with respect to thecleaning cup assembly 68. FIGS. 39A, 39B, and 39C correlate to thepositions of the conditioning arm 62 in FIGS. 36A, 36B, and 36C. In thisembodiment of the use of the invention, the conditioner head 64 sweepsacross the polishing platen 52 in a coordinated motion with the waferhead 110 during the simultaneous polishing and conditioning operation.The coordination is required to avoid interference with the wafer head110 as it radially oscillates in the slot 910 of the carousel supportplate 90.

In the plan view of FIG. 39A, the wafer head 110 is generally centeredon the polishing pad 54 with the conditioner arm 62 located in itsstorage position with the conditioner head cleaning cup assembly 68surrounding the conditioner head 64.

In FIG. 39B, the conditioner arm 62 is being pivoted vertically out ofthe cleaning cup assembly 68 and a phantom line 2640 shows the extremeouter position of both the wafer head from an inner extreme to an outerextreme without overlapping the platen edge while another phantom line2642 shows a similar oscillation between inner and outer extremes forthe conditioning arm 62.

In FIG. 39C, the cleaning cup assembly 68 has been moved out of the pathin which the conditioner arm 62 travels during its oscillating swingacross the polishing pad 54 from the center to the edge and back. Notethat the wafer head 110, the conditioner head 64, and the platen 52 allrotate in the same (clockwise) direction. FIG. 39C shows an outerextreme position of the wafer head 110 when the head is allowed to hangover the edge of the platen 52. The retaining ring portion of the waferhead 110, but not the wafer held by wafer head, is allowed to hang overthe edge of the platen 52.

In an alternative process, the conditioning and polishing steps areseparated. During the polishing process, the conditioner head 64 isstored in the storage cup assembly 68, as generally illustrated in FIG.39B, while the wafer head 110 is sweeping the wafer 40 across therotating polishing pad 54. During the conditioning process, as generallyillustrated in FIG. 39C, the wafer head 110 is stored at its innermostposition nearest the center of the carousel 70 and above the rotatingpad 54. The conditioner head 64 is lifted from the storage cup assembly68, which is rotated to a non-interfering position, and the conditionerhead 64 is swept over the rotating pad 54 to thereby condition it. Whenthe pad conditioning is completed, the cup assembly is rotated back to aposition at which the conditioning head 64 is returned to be stored init.

Wafer Transfer Alignment and Cleaning Station

Referring back to FIGS. 1 and 2, the transfer station 70 serves themultiple purposes both of transferring the wafer back and forth betweenthe loading apparatus 30 and the polishing apparatus 20 and washing thewafer after its polishing has been completed. FIG. 40 shows an enlargedperspective view of the wafer transfer station 70, which is raisablewith respect to the table top 23. A wafer transfer pedestal 72 has a topsurface extending generally horizontally to which a thin elastomericfilm 722 is adhered for gently supporting a wafer on top of the pedestal72 without scratching its principal surface. Three fork assemblies 74are disposed around one vertical position of the pedestal 72 tolaterally align the wafer supported on the pedestal 72. The pedestal 72is vertically retractable within a washing shroud 76 so that, when threewashing assemblies 77 attached to the shroud 76 jet rinse fluid towardthe wafer, pedestal, or wafer head, the rinse fluid is contained withinthe shroud 76. The shroud 76 is also vertically raisable with respect tothe table top 23.

FIG. 41 shows a plan view of the top of the platen and of the washingshroud. FIGS. 42 and 43 show perspective views at two different anglessimilar to FIG. 40, but partly in cross section to show the operation ofthe forks and water nozzles. FIG. 44 shows a detailed cross-sectionalview of the pedestal area of the transfer station. The shroud 76 issupported on and sealed to a generally cylindrical basin shaft housing78 while the pedestal is threaded on and supported by a tubular pedestalcolumn 79 extending vertically within the basin housing 78.

Wash and Vacuum Ports on Pedestal and in Wash Basin

The pedestal 72 of the transfer station 70, as illustrated in the plantop view of FIG. 41 and the cross section of FIG. 44, includes bothcentral ports 724 and multiple offset ports 726 on the top surface ofthe pedestal 72 offset from its center and penetrating the elastomericfilm 722. That is, the ports 724 and 726 for water and vacuum openthrough the top of the pedestal 72 and the elastomeric film 722. Theports 724 and 726 are connected to lateral passageways 728 in thepedestal 72 (only two of which are illustrated in the cross section ofFIG. 44) connecting to a vertical passageway 730 in opposition to acentral passageway 732 in the tubular pedestal column 79. Eitherpressurized wash fluid or a vacuum is applied to the bottom of thecentral passageway 732 in the pedestal column 79 through a flexiblefluid hose 736 detachably coupled to the pedestal column 79 through athreaded union 738. In order to avoid contamination of the vacuum sourcewith the wash fluid, a vacuum generator and a three-way valve areconnected to the flexible line 736 at its junction with the vacuum lineand the wash supply line. The vacuum generator uses water pressure togenerate a generate a vacuum. An exemplary vacuum generator is a ModelL10 vacuum pump available from PIAB of Hingham, Mass. Through thethree-way valve, the central passageway 723 of the pedestal column 79and its associated ports can be supplied with pressurized liquid or avacuum with reduced possibility of the vacuum source being contaminatedwith the liquid.

As shown in the plan view of FIG. 41 and in the side sectional view ofFIG. 49A, disk tip nozzles are screwed into the ports 724 and 726,preferably Model 680.345.17 available from Lechler of St. Charles, Ill.A one-way check valve, to be described later, is installed in thecentral port 724 to prevent wash fluid from being ejected therefrom butto allow vacuum to be pulled at the central port. When a pressurizedcleaning solution is supplied through the offset ports 726, the upwardlydirected liquid cleans a bottom surface of a wafer head 110 and anywafer adhered thereto. When a wafer is in contact with the elastomericfilm 722, a vacuum supplied to the ports 724 and 726 seals the wafertightly to the top of the pedestal 72.

The three washing assemblies 77, illustrated both in perspective andcross section in FIG. 43, are disposed at about 120° intervals about thepedestal 72 and generally disposed in the periphery of the shroud 76beneath a porch roof 740 and inside an outer wall 741. Each washingassembly 77 includes a lower member 742 fixed to an inside bottom 743 ofthe basin 76 and having a radial passageway 744 connecting to a firsttapped nozzle hole 746 through a vertical passageway 748. The washingassembly 77 further includes an upper member 750 fixed on the lowermember 742 and having its own vertical passageway 752 sealed to theother vertical passageway 748 and connecting to a second tapped nozzlehole 754. Respective flat-spray nozzles are screwed into the nozzleholes 746 and 754 with their respective slit orientations chosen tooptimize the overall spray pattern. The lower nozzle hole 746 has alongitudinal axis directed upwardly by about 30° with respect to thehorizontal plane of the pedestal 72, and the upper nozzle hole 754 hasits longitudinal axis directed downwardly by about 15°; that is, the twonozzle holes 746 and 754 are offset from the plane of the wafer 40 by anangle in the range of approximately 10° to 45°. The offset of these twospray patterns may be arranged to intersect near to or outside theperiphery of the pedestal 72 so as to more effectively wash the emptypedestal 72 and the wafer held by the polish.

As shown both in FIGS. 43 and 44, each washing assembly 77 furtherincludes a supply tube 756 connected to the radially inner end of thelower member 742 and sealed to its radial passageway 744. The supplytube 756 of each washing assembly 78 runs vertically down the inside ofthe basin housing 78 to its lower end. At this point, it is joined to apassageway 758 in a lower collar 760 that has a tapped hole on its outerwall for a threaded connection to a flexible line for the wash fluid.

Thus, wash fluid can be independently supplied to the three generallyhorizontally oriented peripheral washing assemblies 78 and to thevertically oriented ports 726 on the top of the pedestal 72. The washingfluid from either source is substantially contained within the basinshroud 76 when the wafer head 110 is positioned over the transferstation 70 and the basin shroud 76 and associated washing assemblies 77are raised to place the wafer head 110 and the attached wafer inside theporch roof 740 of the basin shroud 76. Excess washing fluid andentrained slurry are caught within the basin shroud 76 and draindownwardly toward the bottom of basin housing 78 where a drain passage759 penetrates the bottom of the basin housing 78 and the collar 760 andconnects to a drain pipe 761.

The raising of the basin shroud 76 around the wafer head 110 reduces thevertical stroke required of the wafer head 110. This short strokecontributes to a simpler and lighter design for the wafer head.

Wafer Alignment Forks

As illustrated generally in FIG. 40 and as will be explained in moredetail later, the three fork assemblies 74 are used to align the waferhead 110 relative to the washing station 70 and its pedestal 72 afterthe wafer 40 has been loaded onto the pedestal 72 by the wafer transferpaddle. Then, the pedestal 72 is slightly lowered and the basin shroud76 with attached fork assemblies 74 is significantly raised to laterallysurround the pedestal 72, wafer 40, and the lower portion of the waferhead 110. Only after the centering is completed is the wafer 40 loadedinto the wafer head 110.

FIG. 41 also shows in plan view the triangular orientation of the threewafer alignment fork assemblies 74. As additionally shown in theperspective view of FIG. 42, the expanded perspective and partiallysectioned view of FIG. 45, and in the cross-sectional view of FIG. 44,each fork assembly 74 includes a fork 762 rotatable within a limitedangular range and having a pair of alignment tines 764 for abutting theedge of the wafer to be centered. The fork 762 rotates on the distal endof a radially extending fork arm 766 having its proximal end fixed to avertical rib 768 extending down the interior of the basin housing 78.The lower end of the rib 768 is hinged about a shaft 769 to a wing 770of a support sleeve 772, to be described later, that is fixed to thebasin housing 78. A pneumatic cylinder 774 is fixed to a side of theoutside of the basin housing 78 and has an output shaft 776 penetratingthe basin housing 78 and having on its shaft end a coupling threadedinto a middle portion of the vertical rib 768. Although the presentdesign dedicates one pneumatic cylinder 774 to each rib 768 andassociated fork assembly 74, the design could easily be modified toactuate the three ribs 768 with one pneumatic cylinder.

The pneumatic actuation and deactuation of the fork pneumatic cylinder774 controls the radial position of the fork 762 relative to the waferon the pedestal 72. Actuation presses the rib 768 radially inward so asto cause the fork 762 to approach and possibly touch the wafer on thepedestal 72. Deactuation pulls the rib 768 radially outward so as towithdraw the fork 762 from the pedestal 72. It is noted that thegeometry couples radial motion of the forks 762 with an axial motion ofthem so that the forks 762 rise as they approach a wafer 40. The forkpneumatic cylinder 774 is spring loaded so as to present a varying loadto the pneumatic cylinder 774 and thus to allow a finer pneumaticcontrol of position. A detent screw 778 is threaded from the bottomthrough a radially inner portion of the fork arm 766 so as to provide avertically adjustable lower stop to the fork arm 766 and thus limit theradially outward travel of the fork 762.

As best illustrated in FIGS. 42 and 45, the fork 762 of the forkassembly 74 is rotatably supported on a fork rotation shaft 780 fixed toand extending vertically upward from the distal end of the fork arm 766.Two bushings 782 (only one of which is illustrated in FIG. 45, seize theyoke of the fork 762 and provide free rotation in the horizontal planerelative to the fork rotation shaft 780. The free rotation of the fork762 allows the fork 762 to approach a badly misaligned wafer withminimal scraping action and thus provide six points of contact ratherthan three.

Two bumper assemblies 784 are rotatably supported about vertical axesgenerally radially in back of the fork tines 764. Each bumper assembly784 has two ball bearings allowing free rotation in the horizontal planeof a knob-shaped bumper 786. The bumper 786 engages the side of thewafer head 110, which may not be precisely aligned with the pedestal 92of the washing station 70. After a fork 762 has initially contacted theside of the wafer 110 with both its tines 764, further inward retractionof the fork assemblies 74 causes the unbraked carousel support plate 906to rotate in the required direction so as to bring it into properalignment with the pedestal 72. Only then is the carousel 90 locked inplace. The bumper 786 also realigns any badly misaligned wafer 40.

The cantilevered design of the fork arm 766 and rib 768 pivoted about aremote shaft 769 has the disadvantage that the long moment arm andlimited rigidity of the intervening support structure would allow thefork 762 to wander in both the circumferential and vertical directions.To prevent such wander but without preventing the substantially freemovement of the fork assembly 74, each of three alignment forkassemblies 790 is screwed into a respective recess of and fixed to theouter wall 741 of the wash basin 76 at a circumferential positionsseparated by 120° and axial positions. These positions correspond to apost 792 fixed to and downwardly descending from the fork 762 at aposition radially inward from both the fork rotation shaft 780 and thebumpers 786. The alignment fork assembly 790 has two tines 794 extendingradially inward from the basin wall 741 so as to very loosely capturethe downwardly descending post 792 of the fork rotation shaft 780 andthereby prevent the fork 762 from wandering in the circumferentialdirection by rotating beyond certain predetermined rotational limits.The fork 762 rotates about its bushing 782 within the tines 794 untilits rotation is stopped by the post 792 engaging one or the other of thetines 794.

The above design for the wafer support, in which the process side of thewafer lies on the pedestal, runs counter to the conventional designphilosophy of not unnecessarily contacting the process side of a wafer.An alternative design that avoids such contact includes three fingersextending upwardly from the face of the pedestal and positioned toengage either the rim of the wafer or the outermost periphery of theprocess side of the wafer. Ledges or tapers face inwardly at the uppertips of the fingers to promote alignment of the wafer with the fingers.Thereby, the central portion of the process side of the wafer is leftsuspended over the pedestal. A reflective optical sensor is incorporatedinto the face of the pedestal to sense when a wafer has been placed onthe fingers.

Transfer Station Support and Movement

As previously mentioned and as best illustrated in the cross section ofFIG. 44, both the transfer pedestal 72 and the wash basin 76 areindependently movable vertically with respect to the table top 23 of themachine base 22.

The basin housing 78 freely passes through an aperture 1712 in ashoulder 1714 fixed on top of the table top 23. A pneumatic cylinder1716 is fixed to a side of the lower end of the basin housing 78. Itsoutput shaft 1718 extends vertically upwards, and its foot 1720 iscaptured in a jaw 1722 attached to the bottom of the shoulder 1714through a plate 1724. The basin pneumatic cylinder 1716 thus providesfor relative motion of the basin housing 78, and the elements attachedthereto relative to the table top 23. The pneumatic cylinder 1716 alsomoves the pedestal 92 but separate motive means moved by the pneumaticcylinder 1716 can move pedestal 92 independently of the basin housing78. An unillustrated vertical rail is attached to the shroud 1714, andan unillustrated hand attached to the basin housing 78 engages the railso as to provide lateral stability to the basin housing 78 as it isbeing vertically moved by the basin pneumatic cylinder 1716.

A bottom inward lip 1726 of the basin housing 78 supports the bottom ofthe support sleeve 772 extending upwardly within the basin housing 78.Two cylindrical tursite bushings 1728 and 1730 are interposed betweenthe support sleeve 772 and the pedestal column 79 so as to support it inthe lateral direction but to freely guide it in the vertical direction.The upper bushing 1728 is pressed downwardly against the support sleeveby a collar 1732 screwed into the sleeve 772. The lower bushing 1730only abuts a lower end of the support sleeve 772 and is heldthereagainst and against the pedestal support column 79 by the lowercollar 760. An unillustrated set of bolts pass through the lower collar760, the lower lip 1726 of the basin housing 78, and are threaded intothe lower end of the support sleeve 772 so as to rigidly join the basinhousing 78 and the support sleeve 772. As mentioned previously, for eachfork assembly 74, the rib 768 is pivoted on the shaft 769 passingthrough the wing 770 at the lower end of the support sleeve 772.

The pedestal column 79 and thus the pedestal 72 is movably held to thebottom of the basin housing 78 by a three-legged spider 1740 shownadditionally in perspective in FIG. 46. The spider 1740 is rigidly heldto the pedestal column by two O-rings 1742, shown in the enlarged crosssection of FIG. 44A, with a wedge-shaped spacer 1743 placedtherebetween, all placed in an annular recess 1744 having a lowertapered edge. Axial compression forces the O-rings 1742 into elasticcontact with the spider 1740, the wedge-shaped spacer 1743, and thepedestal column 79, thereby fixing them together. The lip of anoverlying collar 1746 is biased by screws against the spider 1740 so asto force the O-rings 1742 into the acute points of the respective tapersand thereby radially engage the pedestal column 79 and prevent anyrelative motion therewith.

As illustrated in both FIGS. 44 and 46A, each leg 1750 of the spider1740 has at its distal end a jaw structure comprising a lower jaw 1752and a bifurcated upper jaw 1754 with a slit 1755 between the two teethof the upper jaw 1754. A spider support shaft 1756 passes between theteeth of the upper jaw 1754 and has attached to its lower end a foot1758 that is engaged between the lower and upper jaws 1752 and 1754.

The spider support shaft 1756 is the vertically oriented output shaft ofa pneumatic cylinder 1760 attached to a side of the basin shaft housing78. Thus, the actuation of the pedestal pneumatic cylinder 1760 causesthe pedestal 72 and the wafer supported thereon to move vertically withrespect to the wash basin. Three guide posts 1762 pass through bushings1764 in the arms 1750 of the spider 1740. The upper ends of the guideposts 1762 are fixed to the lower collar 760 of FIG. 44 fixed to thebasin shaft housing 78 to thus provide stability to the movement of thespider 1740 and attached pedestal 72.

The above support and motive mechanism used three pneumatic cylinders1760 to move the pedestal, but it could be easily redesigned for onlyone such pneumatic cylinder.

Wafer Loading to Transfer Stations

In loading a wafer 40 into the polishing system 20 from the loadingsystem, as illustrated in FIG. 47A, the washing basin 76 and itsattached elements are lowered away from the virtually verticallystationary wafer head 110, and the pedestal 72 is lowered somewhat to aposition such that the transfer robot blade 38 with the wafer attachedto its lower side (by a process and with apparatus to be describedlater) can pass beneath the vertically stationary wafer head 110 andabove the pedestal 72. When the wafer blade 38 is centrally located, thepedestal 72 is raised so that its elastomeric surface 722 can gentlyreceive the wafer 40. Thereafter, the pedestal 72 is lowered and thewafer blade 38 is withdrawn. As is illustrated, the wafer 40 mayinitially be badly misaligned with the pedestal 72.

In loading a wafer, the transfer washing basin shroud 76 and itsinternal pieces are lowered away from the wafer transfer pedestal 72. Arobot blade 38, with vacuum chucking holes on its bottom holding thewafer 40, moves the wafer 40 into position, and positions the wafer 40face down above the top of the pedestal 72 extending above the washingbasin 67. The pedestal 72 is then raised to contact the wafer surfaceand the wafer is released from the robot blade 38. The pedestal islowered, or the robot blade is raised slightly, to avoid contact betweenthe wafer and the robot blade as the robot blade 38 is horizontallyrotated out from between the wafer head 110 and the pedestal 72. Thewafer head 110 and the washing basin shroud 76 are then raised (FIG.47B) to surround the perimeter of the wafer head 110.

Thereafter, as illustrated in FIG. 47B, the pedestal 72 is raisedsomewhat but the basin 76 is substantially raised so as to surround thevirtually stationary wafer head 110 and the wafer 40 deposited on thepedestal 72. During this operation, the wafer alignment assemblies 74are in their relaxed, radially outward positions. When the basin shroud76 has been raised so that the wafer 40 is horizontally aligned with thetines 764 of the forks 762, the fork pneumatic cylinders 774 areactuated to cause the fork 764 tines to move toward the center of thepedestal 72 and approach if not touch the periphery of the wafer 40supported on the pedestal 72. The forks 764 will move radially inwardlyuntil their bumper 786 contacts the outside of the wafer head 110. Thiscontact will both cause the two-tined fork 762 to circumferentiallyalign about the fork pivoting post 780. As illustrated in FIGS. 48A and48B, further radially inward motion will align the wafer head 110 withthe center 72a of the pedestal 72 and will also cause the tines 764 toalign the center 40a of the wafer 40 with the center 72a of the pedestal72. The tine 764 initially contacting the wafer 40 will pivot back untilthe opposed tine 764 in the same fork 762 also contacts the wafer 40.Thereafter, the two tines 764 will push the already generally centeredwafer 40 toward the other two forks 762, as illustrated in FIG. 47D,until the bumpers 786 of those other two fork assemblies 74 are stoppedby their contacting the wafer head 110. If the wafer 40 is properlyaligned on the pedestal, the alignment fork 762 and its tines 764 willjust barely touch the wafer 40.

The pushing force generated by the alignment forks 762 to align thewafer 40 to the center of the pedestal 72 for attachment to the waferhead 110 is distributed to several of the six tines 764 of the alignmentforks 762. The pushing force of each fork 762 is distributedsubstantially equally through the yoke to push on the wafer 40 at twopoints. As the wafer 40 moves toward the center of the pedestal 72, thefreedom of the yoke to horizontally rotate to maintain its contact withthe edge of the wafer by pivoting without the necessity of a slidingcontact, reduces stress concentrations at the wafer's edge which mayfracture the wafer and distributes the frictional resistance to slippagebetween the alignment jaw and the wafer over a larger area, therebyreducing the possibility of a localized hang-up due to localdeformations which are greater when the same force is applied over asmaller area. The use of the alignment yoke allows for some rotation andsome slippage of the wafer as the wafer is pushed into alignment withthe wafer head 110.

Once the wafer 40 is in alignment with the wafer head 110, as shown inFIGS. 47D and 26C, the wafer is positioned below the recess 1115 of thelower portion 1110 of the wafer head 110.

Thereafter, the fork actuators 774, as illustrated in FIG. 47E, causethe fork assemblies 74 to radially withdraw. The pedestal 72 is thenraised to lift the wafer 40 into the wafer receiving recess 1115 of thelower portion 1110 of the wafer head 110. The wafer 40 is pressed firmlyagainst the inner principal surface of the wafer receiving recess 1115so that a vacuum or surface-tension attachment between the wafer 40 andthe wafer head 110 can be confirmed before the pedestal 72 is lowered.In some configurations, the wafer head 110 will have vacuum ports in thewafer receiving recess 1115 so that an interlock sensor senses when thevacuum ports are sealed by the wafer 40. This assures that the wafer 40is firmly attached to the wafer head 110 and that the pedestal 72,formerly supporting the wafer 40 from below, can be lowered without fearthat the wafer is not properly attached to the wafer head 110. Thewashing basin 76 is then lowered and the wafer head 110 with the wafer40 now attached is ready to be rotated to the next polishing station forpolishing.

Wafer Cleaning and Unloading from Transfer Station

FIGS. 49A, 49B, 49C, 49A, 49B, and 49C provide side elevational and topviews of the operations performed in flushing the wafer head andremoving the wafer from the wafer head once wafer polishing has beencompleted.

FIGS. 50A, 50B, and 50C show the operation of a check-valve assembly1770 located behind the center nozzle 724 at the center of the pedestal72.

FIGS. 49A and 49A show a polished wafer 40 after polishing has beencompleted still attached to the wafer head 110 surrounded by the washingbasin 76 and facing on its bottom side the pedestal 72. All washing jetsare initiated, that is, all six nozzles 746 and 754 of the three sidewash assemblies 77 and the offset nozzles 726 (but not the centralnozzle 724 because of a check valve to be described below) in thesurface of the pedestal 72 all actively spray deionized water or otherchemical solution at the bottom and part of the sides of the wafer head110 and across the top of the pedestal 72 to clean any particles whichmight have been picked up or have adhered themselves to the wafer head110 and the wafer 40 during the polishing process. The wafer head 110can be rotated during this spraying activity so that all areas and allcrevices on the bottom of the wafer head 110 are flushed and cleaned.The water sprayed in the wash basin 76 drains through the center basinsupport housing 78 and is either recycled or discarded.

A close clearance of approximately 0.168" (4.3 mm) between the outsideof the 3C3 wafer head 110" and the porch roof 74 of the wash basinshroud 76 reduces, if not eliminates, the likelihood that water will besplashed out of the basin shroud 76 into other areas of the machine. Itshould be mentioned that a reduced clearance of 0.146" (3.7 mm) existsbetween the roll of the bumper 786 and the wafer head 110.

As can be seen in FIG. 50A, the check-valve assembly 1770 includes aninsert 1772 screwed into the pedestal 72 behind its center nozzle 724.At the intersection of the vertical passage 730 connecting to centerport 724 at the center of the pedestal 72 and the lateral passages 728 ablock 1774 captures a valve ball 1776 between it and tapered walls 1778at the bottom of the vertical passage 730. As illustrated, pressurizedwater supplied from the central passage 732 of the pedestal column 79forces the ball 1776 against the tapered walls of the vertical passage730 to thereby block the central port 724. This blockage provides a moreeven distribution of water pressure to the non-centrally located ports726 across the pedestal 72. If the check-valve of FIGS. 50A-50C were notin place, a larger proportion of the water to be sprayed would come outthe large center nozzle 724 and less would be directed to the othersmaller offset nozzles 726 in the pedestal 72.

FIGS. 49B and 49B show the next step of the unloading operation. Thepedestal pneumatic cylinder 1760 raises the pedestal 72 into contactwith the wafer 40, and a vacuum source is routed through the bottom ofpedestal column 79 to the fluid passages 728 and 732 which just recentlywere conducting water to the offset spray ports 726. The spray nozzles724 and 726 are now transformed into vacuum suction ports. The elastomerfilm 722 on the top of the pedestal 72 creates a tight seal between thewafer 40 and the top of the pedestal 72. As soon as a vacuum seal issensed in the pedestal vacuum supply passage, by the lowering ofpressure in the vacuum lines, the wafer receiving recess 1115 of thewafer head 110 is supplied with a pressurized gas behind the wafer 40 tomore easily release the wafer 40 from the wafer head 110. Otherwise, avacuum seal to the pedestal 72 would have to compete with the vacuum orother attachment force holding the wafer 40 to the wafer head 110.

Note that in FIG. 50B, the ball 1776 of the check-valve 1770 at thecenter port 724 of the pedestal 72 has fallen to be stopped on the block1774 to thereby open the vertical passage 730 so that vacuum can bedirectly applied to a larger area which includes the center of thepedestal 72.

Once the wafer 40 has been captured by the vacuum on top of the pedestal72, the vacuum of the pedestal is maintained and the pedestal is loweredto a second washing position, illustrated in FIGS. 49C and 49C. Slurryor other particles which were caught behind or next to the wafer 40during the time the wafer 40 was attached to the wafer head 110 are nowexposed, and the nozzles 746 and 754 of the washing assemblies 77 areactivated to spray water across the back of the wafer 40 and into thewafer receiving recess 1115 so that all particulates and slurryparticles can be flushed away. During this second washing step, thewafer head 110 can rotate to provide a more even distribution of thewash water which, in this second washing operation, is coming from onlythe three positions of the side washing assemblies 77 and not from theports on top of the pedestal 72. During the second washing operation, avacuum pressure continues to be ported to the fluid ports 724 and 726 onthe top of the wafer pedestal 72 to prevent the wafer 40 from moving asa result of the force of the moving water flushing its surface. Notethat in FIG. 50C, the ball 1776 of the check-valve 1770 remains in itsopen position. Once the second washing of the wafer 40 on the pedestal72 is complete, the basin pneumatic cylinder 1716 lowers the washingbasin 76, and the pedestal pneumatic cylinder 1760 lowers the pedestal72 by its slight stroke to permit insertion (requiring approximately0.25 inches or 6 mm) of the robot blade 38. The pedestal 72 can then beraised to assure that the robot blade 38 contacts the back of the wafer40. Once the vacuum seal is sensed between the robot blade 38 and theback of the wafer 40, the vacuum in the pedestal 72 is released so thatvacuum forces are not competing in trying to hold the wafer 40. Thepedestal 72 is then lowered and the robot blade 38 is moved to place thenewly polished wafer in a wafer cassette 42 for transport.

Table Top Arrangement

FIG. 52 shows a cross-sectional view through FIG. 2 at Section 52--52showing the position of a first wafer head 110a polishing a wafer (notshown) on the platen 52, rotated by the platen rotation motor 232 andthe position of the various pieces relative to one another. Theoppositely located wafer head 110c is disposed at the transfer station70, at which position the wafer head 110c and the attached wafer arewashed after polishing or alternatively a wafer is loaded into the waferhead 110c once it has been received from the transfer station 70.

When the transfer washing basin shroud 76 is lowered away from the waferhead 110c and the other wafer heads 100 are retracted to their positionthat is uppermost and innermost to the carousel hub 902, the carouselsupport plate 906 is rotated to place the wafer heads in new positions.If there is no inter-station washing the rotation is 90°; forinter-station washing, the rotation is typically about 45°.

The carousel support plate 906 is rotatably supported on the stationarysleeve-like center post 902 through a center post bearing 984. Acarousel drive motor 986 is supported by the center post 902 and itsoutput is connected to a harmonic drive 988, such as unit size 65available from the previously mentioned harmonic drive supplier. Theharmonic drive 988 provides a very high torque multiplication drivewhich can rotate and hold the carousel support plate 906 precisely.

The harmonic drive 988 provides an acceptable rotational velocity toturn the wafer head assemblies between stations. However, the staticholding torque of the harmonic drive 988 is insufficient for holding thecarousel support plate 906 precisely at a particular reference positionfor polishing and transfer of wafers while the wafer heads 100 areengaging the rotating polishing pad 54 at varying radial positions.

To provide additional braking, a gear locking system illustrated inperspective in FIG. 53 may be disposed between the carousel drive motor986 and the harmonic drive 988 on a drive shaft 990 linking the two. Ashaft gear 991 is tightly fixed to the drive shaft 990. A thick firstidler gear 992 is rotatably but tightly radially held on a first idlershaft 993. The upper part of the thick first idler gear 992 is alwaysengaged with the shaft gear 991. A thinner second idler gear 994 freelyrotating on a second idler shaft 995 also always engages the first idlergear 992, usually in the lower section of the first idler gear 992 andout of engagement with the shaft gear 991. However, the second idlershaft 995 is axially translatable by a pneumatic cylinder 996 fixed tothe housing for the gears. When the locking pneumatic cylinder 996 isactuated, the second idler gear 994 slides towards the top of the firstidler gear 992 and also engages the shaft gear 991. This engagementbetween the three gears 991, 992, and 994 prevents any of them frommoving. The second idler shaft 993 together with the second idler shaft995 provides the torque arm preventing any rotation of the drive shaft990.

Alternatively, and perhaps preferably, a disk brake assembly may beused. A rotor disk is attached to the shaft 990, and a caliper has itsarms set on opposite sides of the rotor disk with brake pads on the armsfacing the disk. The caliper is selectively closed with a pneumaticcylinder, and the brake pads on the caliper arms bear against oppositesides of the rotor disk to thereby inhibit further rotation.

Returning to FIG. 52, wiring to the wafer head rotational motors andother electrical devices and fluid lines to the rotary couplings 1042 atthe upper end of the wafer head shafts are routed through a wiring andhose bundle 997 generally entering the carousel covers 908 through awiring opening 998 at its top. This routing avoids interference withwafers and reduces the likelihood that the slurry environment can enterthe cover through the wiring/hose opening 998. Rotation of the carousel90 does not cause binding and constriction of the wiring and tube bundlebecause rotation of the carousel 90 is limited to less than 360°, e.g.,in a four head assembly arrangement, to 270° or 315° if all fourintermediate washing stations are implemented. During sequentialprocessing, a first wafer is loaded on a first head and is progressivelyrotated 90° to each subsequent station until it has reached the thirdstation 270° from the loading position. The next rotation sequenceprogressively would take this first wafer another 90° to return it tothe loading station, but to avoid wire and hose binding andconstriction, the equivalent of a forward (clockwise) rotation of 90°,that is a reverse (counterclockwise) rotation of 270°, is performed tobring the wafer back to the transfer/loading position as discussed abovefor FIGS. 5A-5F and 6A-6D. The second and third wafers to be loaded inthe sequence have their forward advance between polishing stationsinterrupted by the reverse rotation of 270° although the functionalsequencing remains the same.

Loading Apparatus in General

As illustrated in the isometric view of FIG. 1 and as briefly describedpreviously, the loading apparatus 30 moves wafer cassettes 42 betweenthe holding station 32 and the holding tub 34 and also moves theindividual wafers 40 between the cassettes 42 in the holding tub 34 andthe polishing apparatus 20, which has just been completely described inextensive detail. Both sets of movement are effected in part by a wristassembly 37 and in part by the arm 35 descending from the overhead track36.

As additionally illustrated in the partial cross-sectional, partial planside view of FIG. 54, the wrist assembly 37 is held by a descending arm35 descending from a horizontal overhead track 36 along which the arm 35horizontally moves. The wrist assembly 37 uses a wafer blade 38 to movethe wafers 40 and uses a claw 39 to move the cassettes 42. To effectthese various movements, the arm 35 is rotatable about its vertical axisand is extensible and retractable along that vertical axis, and thewrist assembly 37 is rotatable about a horizontal axis, itself beingrotatable in the horizontal plane.

As illustrated in the side cross section of FIG. 54, the arm 35 dependsfrom the overhead track 36 and moves along the track 36 so as to movecassettes between the holding station 42 and the holding tub 34 and tomove individual wafers 40 from various positions within the holding tub34 to a position at which the wafers 40 can be loaded into the polishingapparatus 20.

Details of the loading apparatus 30 will now be presented beginning withblade 38 and claw 39.

Blade and Claw

As illustrated in the exploded perspective view of FIG. 55, the wristassembly 37 includes a claw member 312 including a hub portion 314, theclaw 39 extending radially therefrom, and a blade bracket 316. The claw39 includes, as additionally shown in side plan view of FIG. 57, twoparallel fingers 318 and two fingertips 320 extending perpendicular tothe claw 39. The back of the claw 39 also includes a knuckle ridge 322facing the hub portion 314.

A blade body 324 is secured with countersunk flat screws to an openrecess in the blade bracket 316 such that one side of the blade body 324is flush with a side of the blade bracket 316. The flush side of theblade body 324 includes at its distal end a generally rectangular vacuumrecess 328 communicating via an aperture 330 with a vacuum channel 332,best shown in the upper perspective view of FIG. 56, extending axiallyalong the blade body 324. The aperture 330 is formed, as additionallyillustrated in the bottom plan view of FIG. 60, by milling the vacuumrecess 328 and the vacuum channel 332 from opposite sides of the bladebody 324 to a sum of depths greater than the thickness of the blade body324. As a result, the aperture 330 is formed in the area in which thevacuum channel 332 overlaps the vacuum recess 328. By "bottom" of theblade 38 is meant the side with the vacuum recess 328 for vacuum holdingthe wafer 42 on its lower side as it is loaded to and unloaded from thepolishing apparatus 20.

As shown in the top isometric view of FIG. 56, a surrounding ledge 334is milled around the periphery of the vacuum channel 332. An insert 336is fit onto and welded to the ledge 334 so as to seal the vacuum channel332. However, the insert 336 includes a through hole 338 at its proximalend to provide a vacuum port for the vacuum source. The top plan view ofFIG. 59 shows the insert 336 fitted into the blade body 324. Asillustrated in the bottom perspective of FIG. 55 and the side view ofFIG. 58, a vacuum hole 340 is bored through the blade bracket 316. Avertical end of the vacuum hole 340 overlies and is sealed to thethrough hole 338 in the blade insert 336. A horizontal end of the vacuumhole 340 is connected to a threaded coupling of a vacuum hose 342.Thereby, vacuum applied to the vacuum hose 342 can be used to vacuumchuck a wafer 40 to the blade 30. The vacuum chucking is used both toremove vertically oriented wafers from the cassettes 42 and to hold awafer 40 horizontally on a lower side of the blade 38. The blade 38vacuum chucks a wafer 40 on its substrate backside with the process sidecontaining partially formed circuits being unobstructed. Thereby,mechanical damage to the process side is avoided. The blade 38 dechucksthe wafer 40 process-side down on the soft elastomeric surface 722 ofthe pedestal 72 of the transfer station 70. Because the vacuum chuckingis sometimes done in the liquid of the holding tub 38, the vacuum issupplied by a vacuum generator 343 of the sort described before whichgenerates a negative air pressure from a positive liquid or fluidpressure source powered by positive pneumatic pressure. As mentionedpreviously, such a vacuum generator prevents the contamination of a mainor house vacuum source when a vacuum is being drawn against a liquid.The vacuum generator 343 is fixed on the wheel housing 344 at the sideof the wrist 37. Also attached thereto is an air pressure sensor 345connected to the vacuum hose 342 to sense the pressure within the hose342. This is particularly valuable to sense when the vacuum chuck hasindeed chucked the wafer.

As shown in the isometric drawing of FIG. 61, the claw 39 and blade 38are assembled together into the wrist assembly 37 by screwing the hubportion 312 of the claw 39 to the gear of a gear assembly rotatablysupported in a worm wheel housing 344 that is rotatably andtranslationally supported by the arm 35.

As shown in side plan view in FIG. 57, a worm wheel 346 is fixed to theclaw 39 and blade 38 and is rotatably held on the outer races ballbearing assemblies 348 having inner race fixed to a shaft 350 secured tothe worm wheel housing 344 (see FIG. 61) and outer races fixed to theworm wheel housing 344. As shown in the side plan in FIG. 57 and in thetop cross section in FIG. 61, a worm gear 352 descending vertically fromthe arm 35 engages the worm wheel 346. When the worm gear 352 turns, theblade 38 and claw 39 rotate in a vertical plane about the shaft 350 ofthe worm wheel 346. As will be described in detail later, this rotationis used (1) to exchange the blade 38 and claw 39 from their operativepositions, (2) to rotate the wafers 40, once on the blade 38, betweentheir vertical orientation in the cassettes 42 and their horizontalorientation for their presentation to the polishing apparatus 20, and(3) to engage and disengage the claw 39 from the cassettes 42.

Track and Arm

The discussion now returns to the overhead track 36 and to the arm 35 itsupports. The arm 35 moves horizontally between the cassettes 42 and thewafers 40 contained therein, and it supports, rotates, and verticallymoves the wrist assembly 37.

The overhead track 36 shown in FIG. 1 is covered by a protective cover360. A belt motor 361 protrudes from one end although the motor 361 canadvantageously be placed at the other end.

A carriage 362 rotatably supporting the arm 35 is, as additionally shownin the perspective view of FIG. 62, bolted to a slider 364 horizontallyslidably supported on its one side by a side rail 366 extending linearlyalong the overhead track 36. The rail 366 is affixed to a side of a boxbeam 368, which forms the main support member for the overhead track 36.A cantilever bracket 370 fixed to the top of the slider 364 extends overthe box beam 368 and is itself fixed by two connection points to a drivebelt 372. The drive belt 372 is toothed on its inside and is wrappedaround two toothed sheaves 374 and 376. The first sheave 374, asadditionally illustrated in end perspective in FIG. 63, is attached to ashaft 378 rotatably supported on one side of the box beam 368. Thesecond sheave 376 is similarly supported in a free wheeling fashion onthe same side of the box beam 368. Both end portions of the box channel368 adjacent to the sheaves 374 and 376 have top cut outs 380 throughwhich the sheaves 374 and 376 protrude so that the top part of the drivebelt 372 is led outside of the box beam 368 and the bottom part is ledthrough the interior of the box beam 368.

As illustrated in both isometric views of FIGS. 62 and 63 and in the cutaway top plan view of FIG. 64, a channel-closing belt 380 is wrappedaround two free-wheeling capstans 382 rotating about shafts 384 mountedin side walls of the box channel 368 at positions below the shafts 378of the drive belt sheaves 374 and 376. A ridge 385 in the center of thechannel-closing belt 380 matches corresponding grooves 385a in thecapstans 382 to maintain alignment of the belt 380 as the horizontalslide 364 is moved from end to end.

The ends of the channel-closing belt 380 are fixed to the bottom of thecarriage 362 at an distance from the rail 366 generally corresponding tothe arm 35 and wrist assembly 37. The channel-closing belt 380 thusprovides a sliding seal which closes the bottom of the protective cover360 so that particles do not fall out from the inside of the housingonto wafers being processed nor does slurry contaminate the mechanism.

Various parts 387a, 387b, and 388 shown in the isometric view of FIG. 62extend longitudinally along the track 36 to provide additional supportand covering. As illustrated, the lower corner part 388 and the cover360 provide an open longitudinal slot 389 along which the arm 35 slidesas it depends from the carriage 362. However, the slot 389 allowspolishing debris to penetrate upward into the delicate mechanicalelements of the track 36 and carriage 362 and further allows mechanicalparticles to pass downward to the wafers to thereby contaminate them.The channel-closing belt 380 provides both the function of stabilizingthe carriage 362 as it moves from one end to the other and theadditional function of preventing particulates and debris from insidethe cover 360 from falling down to the wafer 42 and the further functionof protecting the mechanical parts from slurry.

Both the shaft 378 for the free-wheeling sheave 376 for the drive belt372 and the shaft 384 for one of the capstans 382 for thechannel-closing belt 380 are mounted to their respective box-channelwalls by flanges set in longitudinally extending slots in the walls.Each flange is selectively biased by a threaded coupling between it andan anchor post located outboard of the respective slot. Thereby, therespective belt 372 or 380 is selectively tensioned.

As shown best in the axial cross section of FIG. 65, the carriage 362captures the outer race of a circular bearing assembly 390 while aflange 392 of a collar 394 captures the inner race. As will be describedlater, the collar 394 supports the arm 35. A horizontal worm wheel 396is supported by and above the collar 394. As further shown in thevertical plan view of FIG. 64, the worm gear 386 engages the worm wheel396 to thereby rotate the arm 35 and the wrist assembly 37 in thehorizontal plane about the vertical axis of the arm 35.

As shown in both the perspective view of FIG. 62 and the side crosssection of FIG. 54, a flat head plate 390 of an arm C-section 392 isbolted to the bottom of the collar 392 rotatably supported by thecarriage 362. An arm cover 394 encloses the arm 35 while it's in use.

The extension and retraction of the arm 35 is controlled by a worm motor1300, shown in the longitudinal and side views of FIGS. 54 and 65. It ismounted within the carriage 362 and its vertically oriented output shaftis connected to a worm gear 1302 passing downwardly through the collar394 and the head plate 397 of the arm C-section 392 to within the arm35. The vertically descending worm 1302 engages a traveling worm nut1304 in an upper part of an L-bracket 1306. As shown best in theperspective view of FIG. 61, the back of the L-bracket 1306 has a linearbearing dovetail groove engaging a vertical linear bearing rail 1308affixed to a vertical portion 1310 of the C-section 392. The worm drive1300, 1302, 1304 provides a vertical travel of about 101/2 inches (27cm), which is enough to manipulate an 8-inch (200 mm) wafer 40 from acassette 42 and position it atop the pedestal 75 positioned over thetable top 23.

As shown in the side view of FIG. 54 and the perspective of FIG. 61, amotor 1314 is mounted on a foot 1316 of the L-bracket 1306. An outputshaft 1318 passes through the foot 1316 and along the central passage ofa support column 1320. Two half collars 1322, shown in the side planview of FIG. 57 and the perspective view of FIG. 61, fit into an annularrecess 1323 of the support column 1320 and are screwed into the wormwheel housing 344 to fix the support column 1320 at the bottom of thearm 35 to the worm wheel housing 344. The output shaft 1318 penetratesthe worm wheel housing 344 and has the worm gear 352 on its lower endengaging the worm wheel 346 turning the blade 38 and claw 39.

Thereby, rotation by the motor 1314 rotates the blade 38 and the claw 39in the vertical plane, rotation by the motor 384 rotate them rotatesthem in the horizontal plane, rotation by the motor 1300 translates themvertically, and rotation by the motor 361 translates them horizontally,for a total of four degrees of motion.

As shown in the perspective view of FIG. 61, a hollow trombone 1324 isfixed to an ear 1326 of the worm wheel housing 344 and slides throughthe foot 1316 of the C-section 398 into the interior of the arm 35 andparallel to the vertical section 1310. The trombone 1324 bears thenegative pressure pneumatic line 342 (or positive pressure line if alocal vacuum generator is used) and electrical lines led along the shaft350 of the wrist assembly 37 for sensing the absolute angular positionof the blade 38 and claw 39.

Wiring and tubing to the various motors and to the robot blade is routedvia a chain link like rolling wire tray (not shown) positioned in backof the front of and parallel to the track cover 360 of FIG. 62. An endof the rolling wire tray is fixed to a trough in which the fixed end ofthe tray rests. The trough is supported on brackets supporting the trackcover 360. The wiring and tubing is bound to the rolling wire tray, andthe flexible rolling wire tray makes a C-bend before approaching thecarriage 362, to which the other end of the wire tray is fixed. Thesecond end of rolling wire tray follows the carriage 362 as it movesalong the overhead track 36. The wiring and tubing is then routed aroundthe worm drive motor 1300 in the carriage 362 and to the descending arm35 through one or more open holes interspersed with flange bolts aroundthe rotatable collar 394 of FIG. 65 between the carriage 362 and thedescending arm 35. The rotation of the pieces to which wiring or tubingis connected is generally restricted to a rotation in the range of plusand minus approximately 180° so that all angles required for themanipulation of the wafer can be achieved within a back and forth motionwithin the range without excessively binding or constricting the wiringor tubing.

Holding Tub

The details of the holding tub 34 are shown in the axial cross-sectionalview of FIG. 67. The tub 34 itself is an integral body preferably ofpolypropylene or other plastic materials of the sort used in wafercassettes. It includes a generally rectangular outer wall 1430 and aninner weir 1432 of the same shape separated from the outer wall 1430 bya catch basin 1434 and having an outwardly and downwardly tapered top1436 having a tip 1438 below the top 1440 of the outer wall 1430. Thebath 302 is filled into the basin between the inner weir 1432 and isfilled to the tip 1438 of the weir 1432 until it overflows into thecatch basin 1434.

One or more cassettes 42--four appears to be a preferablenumber--holding multiple wafers 40 between their slot ridges 430 areloaded into the tub 34. The top 1438 of the weir 1432 is positioned tobe above the top of the wafers 40 held in the tub 34 and includes, asshown in the side elevational view in FIG. 68, a series of truncatedinverted triangular channels 1438 extending transversely through thewall of the weir 1432. The channels 1438 have bottoms 1439 slightlybelow the intended top level of the bath 302 which is above the top ofthe wafers 40, and these bottoms have widths substantially shorter thanthe average width of the channels 1438. Since only a limited amount ofliquid can flow across the limited width of the bottoms 1439, the levelof the bath 302 typically rises substantially above this level. Thisrise is sufficient to overcome any non-uniformity or elevationaldifferences between the channels 1438 and thereby prevents the bath 302from draining through only a few of the channels 1438.

Each cassette 42 has legs 1442 which are laterally aligned by two rails1444 fixed to a bottom 1446 of the tub 34 and are held by three pairs ofpins 1448 extending outwardly from the rails 1444. As shown in FIG. 69,the three sets of pins 1448 are vertically displaced along the rails1440 so as to support the cassette 42 at the required angle of 3°.Although this inclination angle seems preferable, other angles up to 10°and possibly 15° would provide similar effects in having the wafers 40being substantially vertical while being held at a definite position andangle. Edges 1450 of the cassette legs 1442 are laterally aligned alongthe rails 1440 by a set of alignment pins 1452 extending from the rails1440 to engage the downwardly disposed edges of the cassette legs 1442.

The basin of the tub 34 includes a drain hole 1454 at its bottom, andsupply tubes 1456 extend longitudinally along the rails 1440 at thebottom corners of the tub 34. The bottom corners along the supply tubes1456 are curved and material 1457 is filled into acute corners toprevent accumulation of debris in the corners. The supply tube 1456includes several nozzle holes 1458 directed toward the center of thebasin and a supply passage 1460 penetrating to beneath the tub bottom1446. The catch basin 1434 includes an overflow drain 1460 at its bottomto drain bath water 302 overflowing the weir 1438. A fluid level sensor1464 is fixed to the outer wall 1430 and positioned to sense the levelof the bath 302 at and a few inches below the top 1438 of the weir 1432.

The plumbing is located beneath the tub bottom 1446, and itsconfiguration depends on the desired process, for example continuousoverflow, recirculation, or continuous drain. A typical configurationshown in FIG. 67 includes fresh bath water being supplied through asupply inlet 1466 through a three-way valve 1468 to a pump 1470 pumpingthe bath water through a filter 1471 to the longitudinal supply tubes1456 and from there into the basin. When the level sensor 1464 detectsthat the basin has been filled to overflowing, that is, to the top 1438of the weir 1436, the three-way valve 1468 is switched to insteadrecirculate the overflow water in the catch basin 1434 draining from theoverflow drain 1460. Periodically the basin is drained by turning on adrain pump 1472 selectively pumping bath water from the bottom drain1454 to a tub drain 1474, and then the basin is refilled from the supplyinlet 1466, as described above. Alternatively, on a more frequent basis,the basin is only partially emptied and then topped off with fresh bathwater. The drain pump 1472 is additionally useful when an operatordesires to manually lift a cassette 42 from the tub 34. The bath 302 maybe corrosive so it is desirable that its level be temporarily lowered toallow the operator to grasp the top of the cassette 42. Thereafter, thebasin is refilled.

Other plumbing configurations are possible. To assure recirculation, therecirculation pump 1470 can have its inlet connected to the basin drain1454. If recirculation is not desired, the catch basin 1434 can bedrained externally and only fresh bath water be supplied to thelongitudinal supply tube 1458.

The tub 34 can be improved in at least two ways. First, the catch basin1434 is narrow and deep, making it difficult to clean. An equallyeffective catch basin would be a relatively shallow hanging channelpositioned outboard and just below the top of the weir 1432. Secondly,the recirculation flow can be made more uniform and predictable if aperforated horizontal plate were placed between the bottom of thecassette 42 and the drain hole 1454 so that the pump 1472 pulled bathliquid from a wider area of the tub 34.

Operation of the Loading Apparatus

The operation of the loading apparatus 30 will now be described. Asillustrated very generally in the perspective view of FIG. 1 and in theend view of FIG. 66, the loading apparatus performs two functions withthe same equipment.

First, the wafer blade 38 in conjunction with the arm 35 depending fromthe overhead track 36 loads individual wafers 40 from multiple wafercassettes 42 stored in a bath 302 filled into a holding tub 34. Eachcassette 42 holds multiple wafers 40 in a generally vertical orientationby means of shallow vertical slots formed in opposed vertical walls ofthe cassette 42 such that two opposed edges of the wafers 42 arecaptured in two opposed slots (see FIGS. 67 and 71A). The cassettes 42are commercially available, for example, from Fluoroware. They aretypically formed of polypropylene or PVDF plastic so as to not abradethe wafers 40 and to be chemically inert for the liquids being used. Thebath 302 is composed of a liquid, such as deionized water, whichprevents any adhering slurry from hardening on the wafer. Also, when CMPof a metal layer is performed, the bath protects the fresh metal surfacefrom air, which would oxidize it. Although only a single holding tub 34is illustrated and described in detail, it is understood that multipleholding tubs can be used, especially one for loading unpolished wafersto the polishing apparatus 20 and one for unloading polished waferstherefrom.

Secondly, the claw 39 in conjunction with arm 35 transfers entirecassettes 42 between the holding tub 34 and a holding station 32 alongthe longitudinal direction of the overhead track 36. It is anticipatedthat an operator or automatic transfer apparatus places cassettes 42filled with wafers 40 to be polished at precisely indexed positions atthe holding station 32 and removes therefrom such cassettes 42 filledwith polished wafers 40. However, further automation is possible,particularly for a post-polishing cleaning step.

Wafer Loading

FIGS. 70A, 70B, 70C, 70D, and 70E are general isometric views showingthe sequence of the loading operation in which the robot blade 38 picksa wafer 40 from one of several cassettes 42 positioned within theholding tub 34 (not illustrated in these drawings for sake of clarity)and depositing it onto the transfer station 70 atop the machine base 22of the polishing apparatus 20. The unloading operation of transferring awafer 40 from the transfer station 70 back to a cassette 42 operates inreverse from the illustrated sequence.

During the sequence of these operations, the basin shroud 76 of thetransfer station 70 is withdrawn downwardly within the machine base 22,and, at least during the actual wafer transfer, the transfer pedestal 72is raised upwardly to protrude above both the table top 23 of themachine base 22 and the top of the shroud 76. Also, during this seriesof operations, one of the arms of the carousel support plate 906 ispositioned over the transfer station 70, and an unillustrated wafer headsystem 100 is positioned within the slot 910 of the carousel supportplate 906 overlying the transfer pedestal 72. With the lowermost memberof the wafer head 100 of FIG. 9, that is, the floater member 1112,retracted upwardly to within the bowl member 1110 of the wafer head 110,sufficient clearance exists between the top of the transfer pedestal 72and the floater member 1112 for the wafer blade 82 and attached wafer 40to be manipulated therebetween. Although this requirement is severe, theshort vertical stroke of the wafer head system 100 simplifies the systemdesign and reduces the mass of the carousel 90. Also, since one of thewafer head systems 100 is positioned over transfer station 70 during thetransfer operation, polishing can continue with the three other waferhead systems 100 during the transfer and washing operations, thusincreasing system throughput.

The loading operation begins, as illustrated in FIG. 70A, by moving thearm 35 linearly along the overhead track 36 so that the downwardlydirected blade 38 is positioned over the selected wafer 40 in theselected cassette 42. As mentioned previously, during the loading andunloading operations, the cassettes 42 are submerged in the holding tub34. The cassettes 42 within the holding tub 34 are supported on inclines420 at about 3° from vertical. The orientation is such that the deviceside of the wafers 40 face slightly upwardly and away from the slotridges 430 illustrated in FIGS. 67 and 71A which hold the wafers uprightwithin the cassette 42. The precise linear position of the arm 34 alongthe overhead track 36 is controlled to fit the wafer blade 38 on thesubstrate side of the selected wafer 40 between it and the neighboringwafer or cassette wall and with the vacuum recess 328 of the blade 38parallel to and facing the substrate side. The generally downwardorientation of the blade 38 at the requisite 3° offset parallel to thestored wafers 40 puts the claw 39 in a generally horizontal position soas not to interfere.

The arm 34 is then lowered into the bath 302 along a direction slightlyoffset from the vertical so that the wafer 40 is roughly aligned on thewafer blade 38, as illustrated in FIG. 70B. The inclined path requires acoordinated motion in two dimension. Vacuum is applied to the vacuumrecess 328 of the blade 38 while it is still separated from the wafer.The arm 35 then slowly moves the blade toward the selected stored wafer40. When the vacuum sensor 345 of FIG. 58 senses a vacuum, the wafer hasbeen vacuum chucked and the linear motion of the arm 35 stops. Althoughsome of the bath liquid is sucked in before contact, once the wafer 40is chucked, there is little leakage and that leakage is accommodated bythe vacuum generator 343.

After completion of vacuum chucking, the arm 35 draws the wafer bladevertically upwards at the 3° offset, as illustrated in FIG. 70C. Oncethe wafer 40 has cleared the cassette 42 and the bath 302, the wristassembly 37 rotates the wafer blade 38 about a horizontal axis to theposition shown in FIG. 70D in which the blade 38 vacuum holds the wafer40 on its lower side with the process side of the wafer 40 facingdownwardly. This orientation of the wafer blade 38 positions the claw 39vertically upwards near the arm 35 so as to not interfere with eitherthe carousel 90 or the machine base 22 including its table top. Also,after the wafer 40 clears the cassette 42 and bath 302, the arm 35 ismoved horizontally along the overhead track 36 to bring the blade 38 andattached wafer 40 in proper position for loading onto the transferstation 70 through the sliding door opening in the clean room wall. Theraising, rotating, and linear motions of the arm 35 can be performedsimultaneously once the wafer 40 is above the bath 302.

When the wafer blade 38 and attached wafer 40 have been orientedhorizontally and properly positioned vertically and linearly along theoverhead track 36, the arm 35 rotates the wafer blade 38 about avertical axis to move the wafer 40 through the opening of the slidingdoor and place it directly over the transfer pedestal 72 and below theoverhanging wafer head system 100, as illustrated in FIG. 70E. Thetransfer pedestal 72 is raised to engage or nearly engage itselastomeric surface 722 with the process side of the wafer 40. The wafer40 is dechucked from the wafer blade 38 by releasing the vacuum to thevacuum recess 328 and is rechucked on the transfer pedestal 72 byapplying vacuum to the ports 724 and 726 on the top of the transferpedestal 72. Once the wafer 40 has been chucked on the pedestal 72, itis lowered, and the arm 35 horizontally rotates the now empty waferblade 38 away from the transfer station 70 and the machine base 22 tocomplete the wafer loading operation. Thereafter, the transfer station70 uses the three claw assemblies 72 to align the wafer 40 on thesurface of the transfer pedestal 72.

Typically, the loading apparatus 30 then prepares to unload anotherwafer from the polishing apparatus 20 after completion of its polishing,carousel rotation, and washing in a series of operation generallyinverse to those described above for loading. It is, however,recommended that in returning a wafer 40 to the cassette 42 in theholding tub 34 the downward motion of the blade 38 be stopped acentimeter or so above the point where the bottom of the wafer 40 isexpected to engage the bottom of the cassette 42 and before the wafer 40would engage the side slots 430 of the cassette 42. At that point, thewafer 40 should be dechucked from the vacuum recess 328 of the blade 38and be left to drop the remaining distance. Precise alignments of thewafer 40 on the blade 38 and of the cassette 42 within the tub aredifficult to achieve. If the wafer 40 were to hit the cassette 42 whilestill vacuum chucked to the fairly massive moving robot arm 35, thecollision could break or at least damage the wafer.

Cassette Loading

The loading apparatus 30 is also used to transfer cassettes 42 betweenthe holding station 32 and the holding tub 34. The claw 39 attached tothe wrist assembly 37 at the bottom of the arm 35 is designed foreffecting this movement.

As illustrated in elevational and partially sectioned views of FIGS.71A, 71B, and 71C, the claw 39 is rotated from the lower end of the arm35 to be vertically and downwardly descending from the arm 35. It isthen positioned to a side of the cassette 42, which for 200 mm wafershas a closed handle 422 extending from a longitudinal side 424 of thecassette 42. As shown in FIG. 71A, the claw 39 is positioned such thatits knuckle ridge 322 passes inside of a back 426 of the handle 422 ofthe cassette 42. Then, as shown in FIG. 71B, the claw 39 is horizontallymoved away from the cassette 42 such that its knuckle ridge 322 is belowthe back 426 of the handle 422. Then, as shown in FIG. 71C, the arm 35further vertically raises the claw 39 so that its knuckle ridge 39engages the bottom of the back 426 of the handle 422 attached to thewafer cassette 42. Further raising of the claw 39 lifts the back 426 andthat side of the cassette 42 such that the cassette tilts and a lowerside engages the fingertip 320 of the claw 39. The rotation of thecassette 42 is limited to an amount sufficient that the knuckle ridge 39and finger tips 320 firmly latch the cassette 42. Any further rotationendangers bumping a neighboring cassette 42 in the crowded tub 34. Inthis configuration, the claw 39 supports the cassette 42 and its wafers40 and can move them to any position longitudinal of the overhead track36. As illustrated, the wafer blade 38 is rotated to a horizontalposition in which it does not interfere with the operation of the claw39.

Unloading of the cassette 42 from the claw 39 is accomplished by the arm35 lowering the cassette 42 against a lower bearing surface such thatcassette 42 untilts and disengages its back 426 of its handle 422 fromthe ridge knuckle 32 at the back of the claw 39 when the arm 35 movesthe claw 39 outwardly from the cassette 39. A lesser inward movement ofthe claw 39 clears it of the back 426 of the handle 422 such that theclaw can be drawn vertically upwardly from the cassette 42, leaving thecassette 42 either at the holding station 32 or within the holding tub34.

These FIGS. 71A, 71B, and 71C also show slot ridges 430 formed insidethe cassette on its bottom wall 432 and two side walls to engage andalign the wafers 40. In one type of wafer cassette to be used with theinvention, the very bottom of the cassette is open to suspend the wafers40 above the legs 1442 of the cassette 42. In this cassette, the slotridges 430 are formed on two 45° oriented bottom walls and the twoopposed side walls.

FIGS. 72A, 72B, and 72C are elevational views showing the movement ofwafer cassettes 42 as they are moved between a position within theholding tub 34 adjacent to the polishing apparatus 20, (from whichwafers 40 from those cassettes 42 are easily raised and rotated into andout of the polishing apparatus 20) and a position at the remote holdingstation 32. Cassettes 42 at the remote cassette holding station 32 carrywafers 40 to be polished as received from earlier processing step and/orprovide already polished wafer in cassettes 42 to a later processingstep.

An example of the movement of cassettes 42 will now be described. Asshown in FIG. 72A, the wrist assembly 37 is rotated so as to place theclaw 39 in downwardly facing orientation with the wafer blade 38positioned horizontally above and generally out of the way for thecassette movement.

The arm 35 is linearly positioned along the overhead track 36 such thatits claw 39 is positioned to pass through the cassette handle 422between its back 426 and the side wall 424 of the cassette 42 that it isto move.

As shown FIG. 72B, the arm 35 vertically displaces the claw 39downwardly at the necessary offset angle to engage the handle 422 ofcassette #1, as shown in the process of FIGS. 71A, 71B, and 71C. The arm35 and attached claw 35 lifts the cassette from a first cassetteposition 1' in the holding tub 34 is deposits it, as illustrated in FIG.72C, at the remote cassette holding station 32. The depositing step atthe holding station 32 is the inverse of the lifting step at the holdingtub 34, as has been described above.

It is anticipated that, as soon as a cassette 42 is deposited at theholding station 32, an operator will manually remove it so as to preventslurry solidification or metal oxidation and soon thereafter replace itwith a cassette of unpolished wafers. In the meantime, the transfer arm35 can be transferring wafers 40 between the holding tub 34 and thetransfer station 70 of the polishing apparatus 20. At a convenient timeafter the operator has deposited a cassette 42 of unpolished wafers 40at the holding station 32, the transfer arm 35 then moves that cassettefrom the holding station 32 into the holding tub 34 in a series ofoperations that are the inverse of those of FIGS. 72A, 72B, and 72C.

The cassettes 42 that are moved between the holding station 32 and theholding tub 34 may be full of wafers or may be empty such thatunpolished wafers are transferred from a full unpolished wafer cassetteto an empty polished wafer receiving cassette, or in any other mannerimaginable by persons of ordinary skill in the art.

Although a single holding station 32 has been described in the preferredembodiments, multiple holding stations are possible. In particular, aseparate holding station may be utilized for unpolished wafers andanother for polished wafers just as different holding tubs may beutilized for polished and unpolished wafers. Although the illustratedholding station accommodated only a single cassette, multiple cassettesmay be accommodated as long as the wafer processing problems forexcessively long storage have been addressed. Further, the differentholding stations may be disposed on different sides of the polishingstation.

The above described polishing system is complex and contains many novelfeatures. Many of these features are inventive of themselves and usefulin applications other than wafer polishing.

Although the described system includes four wafer heads, three polishingstations, and one transfer station, many of the inventive advantages canbe enjoyed by other configurations using lesser or greater numbers ofthese elements.

Although the system has been described in terms of polishingsemiconductor wafers, the term wafer can be used in the broader sense ofany workpiece having a planar surface on at least one side thereof thatrequires polishing. In particular, glass and ceramics substrates andpanels can be polished with the described invention. The workpiece neednot be substantially circular as long as the wafer head is adapted toreceive a non-circular workpiece.

The invention thus provides a polishing method apparatus having a highthroughput of substrates being polished. The relatively simple design ofthe apparatus is mechanically rigid and occupies relatively little floorarea. The polishing apparatus can be nearly completely automated, and itis easy to maintain and repair. The advantages of the design areaccomplished by several novel mechanical parts that are applicable totechnological fields other than polishing.

While the invention has been described with regards to specificembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. An apparatus for polishing at least twosubstrates, comprising:at least two polishing surfaces; a rotatablesupport member; at least two substrate head assemblies suspendable fromsaid support member durring a rotaion of said support member and capableof holding on said substrate head assemblies respective ones of saidsubstrates; a positioning member coupled to said rotatable supportmember to move said support member and thereby position a selected on ofsaid substrate head assemblies over a selected one of said polishingsurfaces; and a transfer station positioned beneath said support memberand capable of receiving substrates, wherein said support member ispositionable by said positioning member to position one said substratehead assemblies adjacent to said transfer station while simultaneouslypositioning another of said substrate head assemblies over one saidpolishing surfaces, said one adjacent substrate head assembly beingoperatively associated with said transfer station to selectivelytransfer a substrate from said transfer station to said one substratehead assembly and from one substrate head assembly to said transferstation.
 2. The apparatus of claim 1, wherein said substrate headassemblies are fixed to said support member and said support membersweeps said substrate head assemblies across said polishing surfacesduring a polishing operation.
 3. The apparatus of claim 2, wherein saidsupport member sweeps said substrate head assemblies over said polishingsurfaces substantially in a radial direction with respect to a rotationdirection of said rotatable support member.
 4. The apparatus of claim 3,wherein said transfer apparatus includes a vertically movable pedestaland a plurality of radially movable finger assemblies contactable with asubstrate sufficiently misaligned on said pedestal.
 5. The apparatus ofclaim 4, further including a washing apparatus including at least onespray arm having jets aligned to spray said substrate.
 6. The apparatusof claim 5, further including a conditioner member positionable on oneof said polishing surfaces.
 7. The apparatus of claim 6, wherein saidconditioner member includes a conditioner face positionable on one ofsaid polishing surfaces, and said face is rotatable about an axisperpendicular to the upper surface of said polishing surface.
 8. Anapparatus for polish processing at leat two substrates, comprising:atleast two polishing surfaces; a rotatable support member; at least twosubstrate head assemblies suspendable from said support member during arotation of said support member and capable of holding respective one ofsaid substrates on said substrate head assemblies; a positioning membercoupled to said support member to rotate said support member and therbyposition a selected one of said substrate head assemblies over aselected on of said polishing surfaces and a transfer position; and atransfer station positioned at said transfer position and capable ofreceiving substrates and including a robot selectively holding andmoving a substrate and in communication with said transfer station,wherein said support member is positionable by said positioning memberto position one of said substrate head assemblies at said transferposition while simultaneously positioning another of said substrate headassemblies over one of said polishing surfaces.
 9. The apparatus ofclaim 1, wherein a relative linear motion is imparted between one ofsaid polishing surfaces and the one substrate head assembly positionedthereover.
 10. The apparatus of claim 1, wherein said rotatable supportmember sweeps said heads across said polishing surfaces during apolishing operation.
 11. The apparatus of claim 10, wherein said supportmember sweeps said heads over said polishing surfaces substantially in aradial direction with respect to a rotation direction of said rotatablesupport member.
 12. The apparatus of claim 11, wherein said transferstation includes a pedestal disposed at said transfer positionunderlying said rotatable support member and wherein said robot ismovable to deposit on and remove a substrate from said pedestal.
 13. Theapparatus of claim 12, wherein said pedestal is movable vertically. 14.The apparatus of claim 13, wherein said robot holding said substrate ismovable beneath a substrate head assembly positioned at said transferposition.
 15. A serial substrate polishing apparatus, comprising:aplurality of respective polishing surfaces mounted on a table top; aplurality of substrate heads holding respective substrates on bottomsides thereof; and a support movably supporting said substrate heads andable to engage each of said substrates held on a respective one of saidsubstrate heads sequentially with a plurality of said polishingsurfaces; wherein said support is rotatable about a rotation axis andsaid substrate heads are supported at different angular positions ofsaid support relative to said rotation axis; and wherein N of saidpolishing surfaces are disposed about said rotation axis and whereinthere are N+1 of said substrate heads.
 16. The serial apparatus of claim15, further comprising a transfer station for loading to and unloadingsubstrates from said substrate heads and wherein said N polishingsurfaces and said transfer station are arranged at equal angularseparations about said rotation axis.
 17. The serial apparatus of claim16, wherein said polishing surfaces are movable parallel to a plane ofsaid table top.
 18. The serial apparatus of claim 17, wherein saidpolishing surfaces are rotatable about respective axes perpendicular tosaid plane of said table top.
 19. The serial apparatus of claim 18,wherein said transfer station additionally includes liquid washingnozzles.
 20. A serial polishing process, comprising the stepsof:mounting a plurality of substrates on respective ones of a pluralityof substrate heads, said substrates heads being supported at respectiveangular positions on a rotatable support member; mounting a plurality ofpolishing surfaces at respective positions on a support structure;rotating said support member in a number of discrete angular steps tosequentially position each of said substrates adjacent to at least twoof said polishing surfaces; and providing relative motion between atleast one of said substrates and one of said polishing surfaces topolish a surface of said one substrate.
 21. The serial polishing methodof claim 20, wherein said polishing surfaces are positioned on saidsupport structure and said angular positions of said substrate heads arepositioned on said rotatable support member such that rotating saidsupport member to a predetermined rotation position causes a pluralityof substrates to be simultaneously positioned adjacent to respectiveones of said polishing surfaces.
 22. The serial polishing method ofclaim 21, further comprising loading and unloading one of saidsubstrates to and from one of said substrate heads at a transfer stationto perform elsewhere said polishing of said surface of said one of saidsubstrates, wherein said transfer station is disposed at a position onsaid support structure such that rotating said support member to saidpredetermined rotation position additionally causes another of saidsubstrates to be simultaneously positioned adjacent to said transferstation.
 23. The serial polishing method of claim 22, wherein saidloading or unloading of said another substrate is performed while saidrelative motion is polishing a surface of said one substrate.
 24. Theserial polishing method of claim 23, further comprising moving saidpolishing surfaces within a plane of a top of said support structure.25. The serial polishing method of claim 24, wherein said moving steprotates said polishing surfaces.
 26. The serial polishing method ofclaim 25, wherein said rotating step sequentially positions each of saidsubstrates adjacent to all of said polishing surfaces.
 27. A polishingapparatus, comprising:a rotatable support rotatable about a centralaxis; at least one substrate support head supportable by said rotatablesupport during a rotation of said support; N polishing surfacespositoned at N of (1) equally angularly spaced station positions aroundsaid central axis, wherein N is equal to or greater than 2; and wherebya selected rotation position of said rotatable support causes a selectedone of said at least one support head to be aligned with a selected oneof the group consisting of said polishing surfaces and said loading andunloading mechanism.
 28. The polishing apparatus of claim 26, whereinthere are (N+1) substrate support heads supported by said rotatablesupport at (N+1) equally angularly spaced support positions around saidcentral axis.
 29. The polishing apparatus of claim 28, furthercomprising a robot selectively transferring wafers to and from apedestal included in said loading and unloading mechanism positioned atsaid (N+1)-th station position.
 30. The polishing apparatus of claim 29,wherein said polishing surfaces are movable within a plane of saidstation positions.
 31. The polishing apparatus of claim 30, wherein saidpolishing surfaces are rotatable.
 32. A polishing apparatus,comprising:a plurality of polishing surfaces arranged in a plane; aplurality of substrate heads capable of selectively holding substrateson bottom sides thereof parallel to said plane; a loading/unloadingstation comprising a pedestal; a support structure capable of moving anyof said substrate heads to overlie any of said polishing surfaces andsaid pedestal; and a vacuum chucking member insertable over saidpedestal and having selective vacuum to selectively dechuck a substrateupon said pedestal to thereby deposit it thereupon and to selectivelychuck a substrate supported on said pedestal to thereby remove ittherefrom.
 33. The polishing apparatus of claim 32, wherein saidpolishing surfaces and said load/unloading stations are arranged in acircle.
 34. 35. The polishing apparatus of claim 34, wherein saidsupport structure comprises a plurality of radial slots along which saidsubstrate heads are radially movable with respect to a center ofrotation of said support structure.
 36. A polishing apparatus,comprising:a loading/unloading station for wafers to be loaded andunloaded to and from the polishing apparatus; N polishing surfaces, Nbeing equal to or greater than one, said N polishing surfaces and saidloading/unloading station being disposed at respective ones of (N+1)positions substantially equally angularly spaced about a first axis; andat least one substrate head for holding a substrate on a bottom thereofbeing movable to overlie any of said N polishing surfaces and saidloading/unloading station.
 37. The polishing apparatus of claim 36,wherein said at least one substrate head includes (N+1) substrate headsfor holding respective substrates on bottoms thereof and all beingmovable to overlie any of said N polishing surfaces and saidloading/unloading station.
 38. The polishing apparatus of claim 37,wherein said N polishing surfaces are movable.
 39. The polishingapparatus of claim 38, wherein said polishing surfaces are rotatableabout respective axes parallel to said first axis.
 40. The polishingapparatus of claim 39, further comprising a carousel rotatable aboutsaid first axis and supporting said (N+1) substrate heads.
 41. Thepolishing apparatus of claim 40, wherein said loading/unloading stationincludes a pedestal and further comprising a movable arm for loading andunloading wafers to and from said pedestal.
 42. The polishing apparatusof claim 41, wherein said movable arm transfers substrates between saidpedestal and a cassette holding a plurality of said substrates.
 43. Thepolishing apparatus of claim 42, wherein N is equal to or greater thantwo.
 44. A polishing method, comprising the steps of:at a firstposition, chucking a substrate to a bottom of a substrate holder; afirst step of moving said substrate holder from said first position toat least one of a plurality of polishing surfaces; holding saidsubstrate by said substrate holder against said one polishing surfacewhile providing relative motion between said substrate holder and saidone polishing surface to thereby polish said substrate; a second step ofmoving said substrate holder from said one polishing surface to saidfirst position after it has been polished, wherein said second movingstep includesa third step of moving said substrate holder from said onepolishing surface to a second one of said polishing surfaces, a secondstep of holding said substrate by said substrate holder against saidsecond polishing surface, and a fourth step of moving said substrateholder from said second polishing surface to said pedestal, and whereinsaid first, third, and fourth moving steps are performed simultaneouslywhile three respective ones of said substrate holders hold threerespective ones of said substrates; and dechucking said substrate fromsaid substrate holder.
 45. The polishing method of claim 44, whereinsaid step of providing relative motion moves said one polishing surface.46. The polishing method of claim 45, wherein said step of providingrelative motion rotates said one polishing surface.
 47. The polishingmethod of claim 46, wherein said step of providing relative motionadditionally rotates said substrate.
 48. The polishing method of claim47, wherein said step of providing relative motion provides relativelinear motion.
 49. The polishing method of claim 48, wherein said stepof providing relative linear motion linearly moves said substrateholder.
 50. The apparatus of claim 1, wherein said substrate headassemblies are supported in said support member during polishing ofrespective ones of said substrates.
 51. The apparatus of claim 8,wherein said substrate head assemblies are supported in said supportmember during polishing of respective ones of said substrates.
 52. Thepolishing apparatus of claim 27, wherein said substrate support head issupported by said rotatable support during a polishing of a substratesupported by said substrate support head.